Photosynthetic and Respiratory Activity of Fruiting Forms within the Cotton Canopy

Abstract

The supply of photosynthates by leaves for reproductive development in cotton (Gossypium hirsutum L.) has been extensively studied. However, the contribution of assimilates derived from the fruiting forms themselves is inconclusive. Field experiments were conducted to document the photosynthetic and respiratory activity of cotton leaves, bracts, and capsule walls from anthesis to fruit maturity. Bracts achieved peak photosynthetic rates of 2.1 micromoles per square meter per second compared with 16.5 micromoles per square meter per second for the subtending leaf. However, unlike the subtending leaf, the bracts did not show a dramatic decline in photosynthesis with increased age, nor was their photosynthesis as sensitive as leaves to low light and water-deficit stress. The capsule wall was only a minor site of 14C02 fixation from the ambient atmosphere. Dark respiration by the developing fruit averaged -18.7 micromoles per square meter per second for 6 days after anthesis and declined to -2.7 micromoles per square meter per second after 40 days. Respiratory loss of CO2 was maximal at -158 micromoles CO2 per fruit per hour at 20 days anthesis. Diumal pattems of dark respiration for the fruit were age dependent and closely correlated with stomatal conductance of the capsule wall. Stomata on the capsule wall of young fruit were functional, but lost this capacity with increasing age. Labeled 14C02 injected into the fruit interior was rapidly assimilated by the capsule wall in the light but not in the dark, while fiber and seed together fixed significant amounts of 14C02 in both the light and dark. These data suggest that cotton fruiting forms, although sites of significant respiratory CO2 loss, do serve a vital role in the recycling of internal CO2 and therein, function as important sources of assimilate for reproductive development.The supply of photosynthate for fruit development in cotton (Gossypium hirsutum L.) requires the contribution of assimilate from several sources (2,4,5,20). Studies have shown that the major suppliers of carbon for fruit development are the leaf subtending the boll, the leaf subtending the adjacent fruiting position, and the leaf subtending the sympodium (14). However, these leaves alone cannot meet the seasonal carbon demand necessary to sustain observed increases in fruit dry weight (9,24). This is particularly true for fruit in the lower canopy where more than 60% of the carbon requirements must be imported (21,24 Few studies have comprehensively examined the photosynthetic and respiratory activity ofleaves, bracts, and the capsule wall of cotton, particularly with respect to their patterns during fruit ontogeny. Understanding the gas-exchange properties of these structures would provide greater insight into their contribution of assimilate for fruit development. Therefore, the objectives of this study were to monitor photosynthesis and respiration during development of cotton fruit, bracts, and subtending leaves, and to determine the relative capacity of these tissues to assim...

Polyamine Metabolism of the Cotton Flower and Its Sub-tending Leaf under Water-Deficit Stress in the Field

“…Stomatal conductance has been reported to greatly decrease under limited water supply conditions [23,24]. Experiments with potted plants have reported that water-deficit stress decreased cotton leaf stomatal conductance [25,26]. In our study, in accordance with the majority of the previous research, significant decreases in leaf stomatal conductance rates of waterstressed plants were observed compared to the control.…”

Evidence for Light-Dependent Recycling of Respired Carbon Dioxide by the Cotton Fruit

“…Whereas this balance of CO2 fluxes may occur in certain legume and grain crops, previous studies have indicated that cotton fruit do not assimilate CO2 from the ambient atmosphere (8,16,23). This lack of CO2 assimilation was recently shown by Wullschleger and Oosterhuis (23) to be related not to an impaired photosynthetic capacity but rather to an overwhelmingly large CO2 gradient from the fruit interior (0.45-1.53% C02, v/v) to the external atmosphere.…”

“…Therefore, a combination of CO2 exchange, stable C isotope, and chlorophyll (Chi) fluorescence techniques were used to examine the recycling of atmospheric C02, these organs nonetheless frequently demonstrate a unique capacity for the reassimilation of internally produced C02, especially that CO2 released via mitochondrial respiration from developing ovules (4, 9). Cereal crops have received the greatest attention in this regard (5, 14, 25), although several studies have dealt with other crops as well (2,11,15,16,23). The efficiency with which fruit are able to conserve respired C for subsequent retranslocation back to the ovule could be an important determinant of yield productivity ( 11).…”

“…Cereal crops have received the greatest attention in this regard (5,14,25), although several studies have dealt with other crops as well (2,11,15,16,23). The efficiency with which fruit are able to conserve respired C for subsequent retranslocation back to the ovule could be an important determinant of yield productivity ( 11).…”

“…We previously documented that diurnal C losses from cotton (Gossypium hirsutum L.) fruit can exceed 55% of the maximum daily C gain of these organs (24) and provided preliminary data concerning a light-dependent mechanism for CO2 reassimilation by the capsule wall (23 …”