Submitted to: Annals Of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/13/2000
Publication Date: 10/20/2000
Citation: WISE, R.R., SASSENRATH COLE, G.F., PERCY, R.G. A COMPARATIVE STUDY OF LEAF ANATOMY IN FIELD-GROWN GOSSYPIUM HIRSUTUM AND G. BARBADENSE.. ANNALS OF BOTANY. 2000. Interpretive Summary: Gossypium hirsutum L. (upland cotton) and G. barbadense l. (Pima cotton) are two of the most important fiber producing cotton species in cultivation. G. hirsutum is grown in the humid southeastern U.S. without irrigation while G. barbadense is grown under irrigation in the dry southwestern U.S. When grown side-by-side in the field, g. hirsutum has higher photosynthetic and transpiration rates (Lu et al. 1997. Aust. J. Plant Physiol. 24, 693-700). The present study was undertaken to determine if the differences in physiology can be explained by leaf and canopy morphology and anatomy. Scanning electron microscopy was used to compare the leaf anatomy of field- grown upland (cv Delta and Pine Land 50) and Pima (cv S6) cotton. As compared to G. hirsutum, mature G. barbadense's leaves are larger and thinner, with a thinner palisade layer. The G. barbadense leaves show significant cupping or curling which allows for a more even absorption of insolation over the course of the day and much more light penetration in to the canopy. Although G. barbadense leaves have a 70-78% higher stomatal density on both the abaxial and the adaxial surfaces, its stomates are only one third the size of G. hirsutum's. This results in G. barbadense only having about 60% of the stomatal surface area per leaf surface area as compared to G. hirsutum. These results are discussed in terms of the influences that leaf morphology and anatomy have on photosynthesis, transpiration, and leaf cooling.
Technical Abstract: The two commercial cultivars of cotton, Gossypium hirsutum (upland cotton) and G. barbadense (Pima cotton) exhibit markedly different strategies for the capture of sunlight. This is evident in the shape of the leaves and architecture of the canopies of the two species. This manuscript presents results from a study examining fundamental anatomical and physiological differences between the two species. Many aspects of plant physiological function are intimately tied to anatomical features. This structure/function relationship may give rise to the observed discrepancies in performance of Pima cotton. While Pima cotton produces a more desirable cotton fiber, the limitations in growing conditions and yield restrict its production in the South West region of the U.S. Cotton Belt. Scanning electron microscopy was used to compare the leaf anatomy of field grown upland and Pima cotton. It was found that Pima leaves are larger and thinner, with a thinner palisade layer. While Pima leaves have a greater stomatal density on both upper and lower leaf surfaces, the stomates are only one third the size of those seen in upland cotton. This results in a lower stomatal surface area per leaf surface area in Pima. This difference supports the results of other studies that found a lower transpirational capacity in Pima. The marked three- dimensional cupping of the Pima leaves may be an adaptation to avoid photoinhibitory damage and reduce the temperature of the leaf surface. Since genetic improvements in Pima have resulted in an increased transpiration capacity, the lower stomatal area may be a limiting factor to the success of Pima.