Distribution Photosynthetic

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1 J. Japan. Soc. Hort. Sci. 59 (1) ; The Effects of Several Rootstocks on Photosynthesis, Distribution of Photosynthetic Product, and Growth of Young Satsuma Mandarin Trees Kunihisa MORINAGA and Shikoku National Agricultural Experiment Station, Fukio IKEDA MAFF. Zentsuji, Kagawa-ken 765 Summary The effects of 14 different rootstocks on leaf photosynthesis, distribution of photosynthetic product, and growth of one-year-old trees of satsuma mandarin (Citrus unshiu Marc. var. Sugiyama) were investigated. It was shown that leaves of satsuma mandarin grafted on trifoliate orange strains, such as `Rubidoux', `Pomeroy', and `USDA' showed higher photosynthetic rates than those on common trifoliate orange (Poncirus trifoliata Raf.) rootstock. However, `Oba' (Large leaf strain), `Barnes', and `sour orange' rootstocks had lower rates. Stomatal density and ribulose-l,5-bisphosphate carboxylase (RuBPCase) activity in leaves seemed to be important factors for photosynthetic capacity. Also, the distribution of photosynthetic product differed among the rootstocks. The greatest value of top-root ratio was measured in `Rubidoux' trifoliate orange rootstock. Among the trifoliate oranges, tree size on `Rubidoux' rootstock was greatest and resulted in the highest dry matter production. This was mainly the result of total photosynthetic capacity of the trees. Introduction There are many studies of the effects of rootstocks on crop activities. Apparently, selected rootstocks improve physiological functions of crops. Hozyo and Park studied the effects of rootstock on photosynthesis (10) and the distribution of photosynthetic product to tuberous roots (11) in grafted sweet potato plants. Takahashi also investigated the effects of rootstocks on photosynthesis in young grafted tomato plants (20). We previously have clarified certain characteristics of photosynthesis by citrus trees in relation to environmental and intrinsic factors (15, 16). In fruit tree cultivation, the use of rootstocks can control tree size and vigor (5, 17). The research of Tukey (21) is a typical example of such a study. In Japan, trifoliate. orange is used as a common rootstock in citrus cultivation. The effects of these rootstocks on the growth of trees (12), the quality of fruit and yield (5, 12), water use (4), hormonal balance (18), and freeze tolerance (3) have been investigated by many research workers. In citrus, moreover, the effects of rootstock on alternate bearing (6) and on activity of vesicular-arbuscular mycorrhiza (9) have Received for publication June 21, been studied. There is much research on the characteristics of various rootstocks in relation to enhancement of fruit quality and the control of tree size, improvement of photosynthetic capacity, and distribution of photosynthetic product. But, there are very few studies on the effects of rootstocks on photosynthesis in citrus (19). Therefore, the purpose of the paper is to clarify the effects of different rootstocks on photosynthetic capacity, distribution of photosynthetic product and growth of satsuma mandarin trees, with the objective of improving fruit quality and productivity. Materials and Methods Satsuma mandarin (Citrus unshiu Marc.) scions were grafted on fourteen 2-year-old rootstocks in Eight rootstocks of trifoliate orange strains (Poncirus trifoliata Raf.) were used, `Barnes', `USDA', `Weber-Forset' (W-F), `Pomeroy', `Oba' (Large leaf strain), `Hiryu' (Flying Dragon), `Togenashi' (Thornless strain), and `Rubidoux'. In addition, `Shiikuwasha' (Citrus depressa Hayata), `Cleopatra mandarin' (C. reshni Hort. ex Tanaka), `sour orange' (C. aurantium L.), `Yuzu' (C. junos Sieb. ex Tanaka), and `Jagatara' (C. sinensis Osbeck) were also used. Common trifoliate orange 29

2 30 K. MORINAGA AND F. IKEDA was chosen as the standard because it is the major rootstock in Japan. Photosynthesis of scion leaves, distribution of photosynthetic product to each organ, and tree growth were investigated in the year after grafting. Photosynthesis of single mature leaves on each of the plants was evaluated using an open gas exchange system (15). Air temperature was 25 C, relative humidity was 70-80%, intensity of illumination was 80-90klx, and the air flow rate was /leaf/mm. For measurements of dark respiration, leaves were placed in a darkened chamber. Other environmental conditions were the same as for photosynthetic rate measurements. The dark respiration rate was added to the apparent photosynthetic rate to obtain the gross photosynthetic rate. Extraction and assay of ribulose-l,5-bisphosphate carboxylase (RuBPCase) were carried out as described by Yamashita (22) modified from Friedrich and Huffaker's method (8). Leaves (0.5 g fr wt) were ground under low temperature with 0.1 g of PVP and 4 ml of 0.2 M TRIS-HC1 buffer (ph 8.0), containing 10 mm 2-mercaptoethanol. The homogenates were centrifuged at 30,000 x g for 10 min, after which the supernatant fractions were used for assay of RuBPCase activity. RuBP- Case activity was measured by incubating 10µl of a leaf extract at 25 C for 2 min with 10 µmol of TRIS (ph 8.0), 1 µmol 2-mercaptoethanol, 1 µmol MgCl2, 2 µmol NaH14CO3 (1 µci), and 0.2 µmol RuBP in a final volume of 220 µl. The reaction was terminated by transferring duplicate 50µl portions of the reaction mixture to counting vials containing 50µl of 10 % trichloroacetic acid. Radioactivity was counted in ACS II with a liquid scintillation spectrometer. Stomatal density was measured from replicas using S.U.M.P. (Suzuki's Universal Macro Printing) method. The degree of green in leaves was measured with a colorimeter as Hunter's `a' value. Results Fig. 1. Relationship of photosynthesis to density of stomata in different rootstock combinations of satsuma mandarin trees. Fig. 2. Relationship of photosynthesis of tree to total dry matter weight in different rootstock combinations of satsuma mandarin trees. Rootstocks had significant effects on photosynthesis of satsuma mandarin scion leaves. Phtosynthetic capacity of trees on `Rubidoux', `Pomeroy', and `USDA' rootstocks increased over 10 % in comparison with those on common trifoliate orange rootstock. On the contrary, photosynthesis of scion leaves on `Barnes', `Jagatara', and `sour orange' rootstocks decreased. Especially in sour orange rootstock, photosynthesis was reduced by 50 % when compared to common trifoliate orange rootstock (Fig. 1). The density of stomata showed a positive correlation with photosynthesis (Fig. 1). Leaves on `Rubidoux' rootstock had the highest density of stomata. Total photosynthetic capacity of entire trees also showed a high positive correlation with total dry matter weight (Fig. 2). Rootstocks had no significant effect on the

3 EFFECTS OF ROOTSTOCKS ON PHOTOSYNTHESIS OF SATSUMA MANDARIN TREES 31 degree of green in scion leaves (Fig. 3). RuBPCase activity was positively correlated with photosynthesis (Fig. 4). Growth of trees on different rootstocks was considerably influenced by rootstock variety. Trees on `Rubidoux' rootstock grew most vigorously, and total dry matter per tree was 92.8 g on the average in `Rubidoux' trifoliate. With `Togenashi' rootstock, the weight was 33.3 g, in large leaf rootstock the weight was 44.0 g, and in common trifoliate orange rootstock total dry weight was 69.8 g. Trees on `Rubidoux' trifoliate rootstock grew three times as much as those on `Togenashi' rootstock (Table 1). The distribution of photosynthetic product was also influenced. Trees on `Togenashi' and `sour orange' rootstocks, which showed graftincompatibility, had a high distribution ratio to roots. But, trees on `Rubidoux' and `Shiikuwasha' rootstocks which showed vigorous growth had a lower distribution ratio to roots (Table 1). Fig 3. of Relationship of photosynthesis leaf green color. of leaf to degree Fig. 4. Relationship of ribulose-1,5-bisphosphote carboxylase activity to photosynthesis with five different rootstocks of satsuma mandarin tree. Table 1. The effects of different rootstocks on growth of satsuma mandarin trees.

4 32 K. MORINAGA AND F. IKEDA Discussion Photosynthesis of scion leaves grafted on various rootstocks varied in comparison with those on common trifoliate orange. Since photosynthesis had a significant positive correlation with stomatal density, this was considered to be one of the most important factors affecting photosynthetic capacity. Beakbane and Majumder (2) also showed that rootstocks influenced the density of stomata in scion leaves, and growth was closely related to the density of stomata. Therefore, the density of stomata might be an index related to photosynthesis of scions. The scion leaves on 'sour orange' rootstock had the lowest photosynthesis. This was highly correlated with low density of stomata of leaves, but graft-incompatibility may also be a factor decreasing photosynthetic capacity in this scionrootstock combination. The extent of green color in leaves (i.e., chlorophyll content) had no correlation with photosynthetic rate. Other factors, other than chlorophyll content, influenced photosynthesis to a greater extent. Photosythetic capacity of scion leaves showed a positive correlation with RuBPCase activity. Consequently, enzymic activity influenced photosynthesis. RuBPCase activity is also correlated with photosynthetic capacity in other crops (14). Barden and Ferree (1) reported that rootstocks of apple trees did not influence photosynthesis of scion leaves. In citrus trees, however, rootstocks did influence photosynthesis of scions. It was assumed that an increase or decrease in photosynthesis was related to morphological factors, such as stomata! density, or to biochemical factors such as RuBPCase activity. Trees on `Rubidoux' rootstock grew most vigorously. But, trees on `Pomeroy' and `W-F' rootstocks which had photosynthetic rates similar to those on `Rubidoux' rootstock showed less growth than those on `Rubidoux' rootstock. It is suggested that this is due to high differentiation of leaves having high photosynthesis on `Rubidoux' rootstock. Trees on `Rubidoux' rootstock had more leaves with high photosynthesis and a larger total leaf area. As a result, the trees produced more total photosynthetic product per tree than those on other rootstocks. Photosynthetic capacity was an excellent prediction parameter for selection of su- perior rootstocks. In some rootstock studies of citrus (5,17), trees on `Rubidoux' rootstock grew more vigorously and had a higher yield/canopy volume among trifoliate orange rootstocks. These data agreed with the present results. It is desirable to combine the scion with rootstock which differentiates more leaves having high photosynthetic rates. As mentioned in results, different rootstocks influenced the distribution of photosynthetic product. The ratio of top-root (T-R) dry matter was the greatest on `Rubidoux' rootstock, The ratio in common trifoliate orange rootstock was 0.67, and in `Togenashi' rootstock, The cause of this difference is not clear from these experiments, but it is supposed that the sink-source relationship (13) in trees is affected by changing rootstocks. The function of the root as a sink decreases with growth of roots on rootstocks having a high T-R ratio, consequently the sink function of the top part increases relatively. Since trees having a high T-R ratio have a higher top part and less root, the root is considered to have high physiological functions and activities. Accordingly, it is suggested that rootstocks influence the distribution of photosynthetic product. Syvertsen and Graham (19) showed that hydraulic conductivity of roots was positively correlated with CO2 exchange rates of leaves in citrus. Thus, the functions and activities of roots also influence photosynthetic capacity and distribution of trees. It is clear that differences among rootstocks influence phtosynthetic rates and hence growth and distribution of photosynthetic products. Consequently, the effect on photosynthesis and distribution of photosynthetic product in trees should be considered as an important selection factor for rootstocks. In this study, the relationship between rootstock and fruit set was not investigated since one-yearold trees were used. Thus, this relationship should be studied in the future. Acknowledgment The authors express their sincere thanks to Prof. Irwin P. Ting, University of California, Riverside, Department of Botany and Plant Sciences, for his critical reading of the manuscript.

5 EFFECTS OF ROOTSTOCKS ON PHOTOSYNT H ESIS OF SATSUMA MANDARIN TREES S Literature Cited BARDEN, J. A. and D. C. FERREE Rootstock does not affect net photosynthesis, dark respiration, specific leaf weight, and transpiration of apple leaves. J. Amer. Soc. Hort. Sci. 104: BEAKBANE, A. B. and P. K. MAJUMDER A relationship between stomatal density and growth potential in apple rootstocks. J. Hort. Sci. 50: BROWN S. K. and J. N. CUMMINS Rootstock influenced peach flower bud survival after a natural freeze. HortScience 23 : CASTLE, W. S. and A. H. KREZDORN Soil water use and apparent root efficiencies of citrus trees on four rootstocks. J. Amer. Soc. Hort. Sci. 102: CASTLE, W. S Citrus rootstocks for tree size control and higher density plantings in Florida. Proc. Fla. State Hort. Soc. 93: EL-ZEFTAWI, B. M. and I. R. THORNTON Effects of rootstocks and fruit stripping on alternate bearing of valencia orange trees. J. Hort. Sci. 50: FERREE, M. E. and J. A. BARDEN The influence of strains and rootstocks on photosynthesis, respiration, and morphology of `Delicious' apple trees. J. Amer. Soc. Hort. Sci. 96: FRIEDRICH, J. W. and R. C. HUFFAKER Photosynthesis, leaf resistances, and ribulose-l,5-bisphosphate carboxylase degradation in senescing barley leaves. Plant Physiol. 65: GRAHAM, J. H. and J. P. SYVERTSEN Influence of vesicular-arbuscular mycorrhiza on the hydraulic conductivity of roots of two citrus rootstocks. New Phytol. 97: Hozyo, Y. and C. Y. PARK Plant production in grafting plants between wild type and improved variety in Ipomoea. Bull. Nat. Ins. Agr. Sci. series D : Hozvo, Y., T. MURATA and T. YOSHIDA The development of tuberous roots in grafting sweet potato plants, Ipomoea batatas Lam. Bull. Nat. Ins. Agr. Sci. series D : HUTCHINSON, D. J. and W. F. BISTLINE Preliminary performance of 7-year-old `Valencia' orange trees on 22 rootstocks. Citrus Industry 64(5) : 35, 38, 39, KADOYA, K Studies on the distribution and diversion of photosynthates within tree parts during the growth of satsuma mandarin fruit. Memoirs of the College of Agr. Ehime Univ. 18. Extra issue. 14. LORIMER, G. H The carboxylation and oxygenation of ribulose-l,5-bisphosphate : the primary events in photosynthesis and photorespiration. Ann. Rev. Plant Physiol. 32: MORINAGA, K., F.IKEDA and T. KIHARA Studies on the photosynthesis and fruit production in citrus. 1. On the different photosynthetic potential in satsuma mandarin leaves. Bull. Shikoku Agr. Exp. Stn. 45: MORINAGA, K., F. IKEDA and T. KIHARA Studies on the photosynthesis and fruit production in citrus. 2. The effects of water stress on photosynthetic rates in satsuma mandarin trees. Bull. Shikoku Agr. Exp. Stn. 45: PHILLIPS, R. L. and W. S. CASTLE Evaluation of twelve rootstocks for dwarfing citrus. J. Amer. Soc. Hort. Sci.102 : STEVENS, G. A., Jr. and M. N. WESTWOOD Fruit set and cytokinin-like activity in the xylem sap of sweet cherry (Prunus avium) as affected by rootstock. Physiol. Plant. 61: SYVERTSEN, J. P. and J. H. GRAHAM Hydraulic conductivity of roots, mineral nutrition, and leaf gas exchange of citrus rootstocks. J. Amer. Soc. Hort. Sci.110 : TAKAHASHI, K Memoir of Prof. TAKA- HASHI's academic achievements. Memorial committee for Prof. TAKAHASHI. 21. TUKEY, H. B Dwarfed fruit trees. Cornell University Press, Ithaca and London. 22. YAMASHITA, T Changes in contents of adenine nucleotides and development of ribulose bisphosphate carboxylase activity during shooting of mulberry saplings. Plant and Cell Physiol. 24:

6 34 K. MORINAGA AND F. IKEDA