Morphometric Analysis of Chloroplasts of Cotton Leaf and Fruiting Organs

We examined morphological and ultrastructural differences in chloroplasts of cotton leaves and the fruiting organs, bract, and capsule wall to advance our understanding of their commonly observed differences in photosynthetic efficiency. Chloroplasts from leaves were large (7.1 μm long in cross section), lens shaped with a well developed membrane system differentiated into grana and stroma lamellae that occupied the large cross-sectional area (12.3 μm²) of the organelle. A few small plastoglobuli and starch grains were scattered in the stroma region. The bract chloroplasts were correlative of leaf chloroplasts in size (6.8 μm in length) and shape with the exception that the bract chloroplasts exhibited greater thylakoid number per granum (15.8) than the leaf chloroplasts (10.5). In contrast to leaf and bract, the capsule wall chloroplasts were smaller in size (4.3 μm) and cross sectional area (6.8 μm²) than either the leaf or bract. The most intriguing feature of the capsule wall chloroplasts was its domination by large starch granules (5.3 μm²) in the stroma which filled the whole chloroplast coercing the membrane system to move towards the periphery of the organelle. Grana number and thylakoids per granum were lowest in the capsule wall chloroplasts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction of Meloidogyne incognita and Water Stress in Two Cotton Cultivars

A series of controlled-environment experiments were conducted to elucidate the effects of Meloidogyne incognita on host physiology and plant-water relations of two cotton (Gossypium hirsutum) cultivars that differed in their susceptibility to nematode infection. Inoculation of M. incognita-resistant cultivar Auburn 634 did not affect growth, stomatal resistance, or components of plant-water potential relative to uninoculated controls. However, nematode infection of the susceptible cultivar Stoneville 506 greatly suppressed water flow through intact roots. This inhibition exceeded 28% on a root-length basis and was similar to that observed as a consequence of severe water stress in a high evaporative demand environment. Nematodes did not affect the components of leaf water potential, stomatal resistance, transpiration, or leaf temperature. However, these factors were affected by the interaction of M. incognita and water stress. Our results indicate that M. incognita infection may alter host-plant water balance and may be a significant factor in early-season stress on cotton seedlings.     

A technique to measure the components of root water potential using screen-caged thermocouple psychrometers

This paper describes a simple method which uses screen-caged thermocouple psychrometers to measure the water potential components of the roots of cotton (Gossypium hirsutum L.) grown in pots of sand or nutrient solution. Water stress was imposed by withholding irrigation from the sand-grown plants. Sampling was conducted inside a humidified chamber to prevent evaporative losses. The results obtained were within the range expected and comparable to the few published values for other plants. The technique enabled the demonstration of osmotic adjustment in cotton leaves and roots. Published with the approval of the Director of the Arkansas Agricultural Experiment Station.     

Effects of frost-hardening and salinity on glutathione and sulfhydryl levels and on glutathione reductase activity in spinach leaves

In frost-hardened spinach leaves ( Spinucea oleracea L. ev. Vroeg Reuzenblad ) an enhanced content of water-soluble non-protein sulfhydryl compounds was observed. The enhancement was due to higher levels of glutathione as well as to other non-protein-bound sulfhydryl compounds. In addition glutathione reductase activity was increased upon hardening. The affinity of the enzyme for oxidized glutathione was slightly lowered during hardening. The significance of glutathione accumulation during frost-hardening is discussed. Exposure of spinach to NaCl-stress did not affect the levels of glutathione and glutathione reductase of the leaves. In addition the kinetic properties of the enzyme remained unaltered by salinity. It is suggested that glutathione and glutathione reductase activity are not involved in adaptation of spinach to saline conditions.