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Schneider, H. 1969. The Anatomy of Citrus. In The Citrus Industry Vol II, Chapter 1, pp. 1-85. Very extensive review of anatomy of citrus, but largely an original work Purpose: Present comprehensive overview of citrus plant structure in classical plant anatomy format How we will use this information! How does anatomy relate to function? What anomalies in anatomy and thereby function occur with biotic or abiotic stresses
Scott, F. M., M. R. Schroeder and F. M. Turrell. 1948. Development, cell shape, suberization of internal surface, and abscission in the leaf of the Valencia orange, Citrus sinensis. Bot. Gaz. 109:381-411. No comprehensive study of leaf development in citrus Other plant leaves studied in relation to specific function Purpose: Provide developmental picture in detail from primordium to abscission (have interspersed Scott & Schneider figures, most of leaf from Scott et al)
Arrangement of leaves, buds and petiole abscission zones on a summer shoot of citrus
Aborted bud at termination of new shoot on citrus. No terminal bud growth, always second or first lateral bud
Scott et al. : Leaf primordia and development at apical meristem of a citrus shoot Note vascular development of main vein
Scott et al: Vascular system arrangement in a citrus leaf Vascular network forming in young leaf blade.
Vascular network in citrus leaf Scott et al: Note terminal net
Vascular network and oil glands in a citrus leaf
Leaf cross section
Palisade parenchyma development 2 layers, chloroplasts around wall?
Initial development past primary wall Scott et al: Stomatal arrangement on lower surface of an orange leaf. Note guard cells, ante and substomatal chambers and plugged antechamber.
Structure function K pumps and pressure points
WHY LOWER HALF?
Two abscission zones?
Rays? Limb structure phloem and cambium
Vascular system in wood phloem: sieve elements & companion cells
K.F. Cossmann. 1939. Citrus roots: Anatomy, osmotic pressure and periodicity of growth. Palestine J. Bot., Rehovot Series. 3:65-103 Controversy as to existence of root hairs on citrus roots Limited citrus species examined in earlier work Purpose: Can conclusions about physiological function be made from root anatomy, particularly regarding physiological sheaths? Do citrus roots have root hairs?
Development of primary and secondary vasular system in roots of citrus - Schneider
Root has endodermis with casparian strip and xylem (phloem) strands developing above root cap Casparian strip infuses wall around endodermal cell walls preventing solution passage through wall, must pass through cytoplasm Solution flow
Castle, W. S. 1978. Citrus root systems: Their structure, function, growth and relationship to tree performance. Proc. Int. Soc. Citriculture 1978; 62-69. Except for Cossmann, little reported about root structure in citrus Opportunity to use scanning electron microscopy Purpose: Review and observation of roots with SEM
Rootcap Root hairs Exposed, sheared cortical cells
Imbedded sand grain
On the relationship between specific root length and the rate of root proliferation: a field study using citrus rootstocks. DAVID M. EISSENSTAT. New Phytol. (1991), 118, 63-68 This study tested two hypotheses: (1) species with roots that have a high length to dry mass ratio or specific root length (SRL) also have the potential for high rates of root growth in small volumes of favourable soil and (2) variation in average root diameter fully accounts for variation in SRL.
M & M The study used 13-year-old 'Valencia' sweet orange [Citrus sinensis (L.) Osbeck] trees budded to rootstocks representing a range of genotypes. Soil cores 7-4 cm in diameter and 14-2 cm deep were extracted from beneath the canopy, and the soil was sieved free of roots and replaced. Root length, diameter and dry weight of the roots in the disturbed soil and adjacent undisturbed soil were evaluated 5, 10, 19 and 40 weeks following soil replacement.
Results Averaged across rootstocks, root length density increased in a linear fashion in the disturbed soil and was comparable to that in the undisturbed soil by 40 weeks. Mean root diameter of the fibrous roots ( < 2 mm) declined with age. Rootstocks with the highest SRL had the most rapid rate of root proliferation (cm cm"^ wk"^) (r = 0-94) and the greatest rate of water extraction at 19 weeks (r = 0 79).
Figure 1. Time course of (a) root length density and {b) mean root diameter of the fibrous roots, averaged across six citrus rootstocks, in disturbed and adjacent undisturbed soil. Roots were sampled at 5, 10, 19 and 40 weeks after disturbance. Bar denotes two SE.
Figure 2. Relative frequency of different size categories of fibrous root diameter in Cleopatra mandarin (CM) and trifoliate orange (TO), sampled 10 weeks after disturbance. Relative frequency for each rootstock was determined from 320 0-5-cm root segments (40 segments x 8 trees).
Table 2. Patterns of allocation of root length, root dry mass and root volume for six citrus rootstocks (8 trees each). Roots were sampled in soil 19 weeks after disturbance
Figure 3. The relationship of root growth rate with specific root length (SRL) for individual trees and (inset) averaged for each rootstock (n = 8 trees/rootstock). Growth rates and SRL were determined by sampling the disturbed soil at 5, 10 and 19 weeks.
Figure 4. The relationship of root length density and gravimetric soil water content 19 weeks after disturbance for individual trees and (inset) averaged for each rootstock (n = 8 trees/rootstock). Sampling was 8 d following a heavy rain. The curve represents the best-fit of the 48 trees using the iteratively solved asymptotic equation, y = a + b (ex +1)
Conclusions Although variation in root diameter contributed to rootstock variation in SRL, the data also suggested that rootstocks of high SRL had roots with lower tissue density than those of low SRL {P < O'OS). The potential trade-offs of constructing root systems of high SRL are discussed.
Anatomical characteristics of roots of citrus rootstocks that vary in speci c root length. D. M. EISSENSTAT and D. S. ACHOR. New Phytol. (1999), 141, 309-321 Among citrus rootstocks, higher specific root length (SRL, root length}d. wt) has been linked to several specific morphological and physiological traits, including smaller average root diameter, higher root hydraulic conductivity and higher rates of root proliferation. It is argued that there can be suites of physiological, morphological and anatomical traits in roots that co-vary with specific root length. Investigations of how root morphology and anatomy are linked to root function, moreover, need to recognize trait variability and the potentially important differences between field- and pot- grown (seedling) roots.
In this study, thickness of the outer tangential exodermal (hypodermal) wall and its suberin layer, number of passage cells, presence of epidermis, and stelar anatomy were examined and related to variation in root diameter of field roots of known maximum age. We also compared root morphology and anatomy of young roots in the field with those of potted rootstock seedlings in the glasshouse. Fibrous roots were measured separately from pioneer (framework) roots. Among the fibrous roots, only the firstorder (root links having a root tip) and second-order (root links bearing first-order roots) laterals were examined.
Figure 1. Transverse sections, 1±5 cm root tip, of first-order citrus fibrous roots from field trees (age 13). (A) Light micrograph of sour orange root showing epidermis (E), exodermis hypodermis, EX), inner cortex (C) and stele (S). An enlargement of an area similar to that in the square is shown in (B). (B) TEM of sour orange epidermis (E), exodermis (Ex) and inner cortex (C). Note thickening of outer tangential wall (L) of the exodermal cells. (C) Light micrograph of transverse section of trifoliate orange first-order root showing the areas indicated above. (D) TEM of trifoliate orange root indicated in square in (C) showing the epidermis, exodermis with passage cells (PC) and inner cortex. The outer tangential wall of the exodermal cells is not as thick in trifoliate orange as in sour orange.
Figure 2. Transmission electron micrographs of transverse sections of field first-order fibrous roots showing the cell wall thickness of the exodermis (Ex). (A) Sour orange. (B) Trifoliate orange. Micrographs taken at same magnifcation to illustrate the typical widths of the lignifed (L) and suberized (S) layers of the outer tangential wall. The area above the wall is a epidermal cell (E) and below the wall is the exodermal cell (E
TO SC SO RL Figure 3. Frequency distribution of root diameter, thickness of the outer tangential wall of the exodermis, thickness of the outer tangential wall of the suberin layer alone, and passage cell number of first-order roots collected from trees in the field. Roots were less than 14 wk old. Trees were Valencia sweet orange on trifoliate orange (TO), sour orange (SO), Swingle citrumelo (SC) and rough lemon (RL) rootstocks. Each frequency distribution represents about 80 roots (10 roots x 8 trees) for each rootstock
Figure 4. The relationship of root diameter with exodermal outer tangential wall thickness and with number of passage cells in the exodermis in first- and second-order roots. Means (SE) of fibrous roots of rootstock genotypes from trees in the field ( ) and from seedlings grown in the glasshouse ( ). Least-squared regression lines presented where the correlation coefficient was significant at P!0±10 (see Table 2).
Figure 5. Percentage of roots of each citrus rootstock genotype of which 0±30 ( ), 30±70 ( ) and 70±100% ( ) of epidermis was still intact. Roots collected from field trees and glasshouse potted seedlings were no older than 14 and 19 wk, respectively.
Among first-order field roots, larger root diameter was caused by larger rather than more numerous cells in the cortex. Root diameter of first-order roots was positively correlated with both number of passage cells in the exodermis and thickness of the secondary walls of the exodermis in both field and potted plants.
Exodermal walls were about 80% thicker in field- than potgrown roots. In the eld, in more than 50% of the firstorder roots examined less than 30% of the root surface was still covered by epidermis, with few differences among rootstocks. In contrast, in roots of 19-wk-old glasshouse plants generally 70±100% of the epidermis was still intact. There was no evidence of secondary xylem development in second-order fibrous roots in the field; in seedling, potgrown rootsystems, 75±97% of second-order roots had formed secondary xylem despite their small diameter (!0±8 mm).
Castle, W. S. and A. H. Krezdorn. 1979. Anatomy and morphology of field-sampled citrus fibrous roots as influenced by sampling depth and rootstock. Hortscience 14:603-605. Citrus root variability by depth is not known Presumed that root morphology, anatomy and function could vary by depth Purpose: Examine and compare anatomy and morphology of roots from 4 rootstocks at 3 depths (no hypothesis except inferred that root function differs by depth) should look at references implicated
Range of root distrbutions, ie. Rough lemon versus Cleopatra mandarin
Like rough lemon Poorer growth than seedling
Summary Good information on root distribution Clearly described pioneer versus fiberous roots No overall root system pictures for Swingle No information about objective of root anatomy differences with depth
Fate of tap roots -- FEEDER ROOTS MUCH HEAVIER IN TOP FOOT