Distribution of 14c Label From Cotton Leaves: Consequences of Changed Water and Nitrogen Status.

Abstract

14CO2 was applied to individual cotton leaves and its distribution after 24 h was examined in plants of varying water and nitrogen status. Redistribution patterns as well as leaf net photosynthesis and leaf expansion patterns were also established. Irrespective of growth conditions, phyllotaxis had a marked effect on distribution patterns. For example, fruit in vertical alignment with the labelled leaf received 2-4 times more label than fruit on the opposite side of the mainstem. Distance of a sink from the labelled source, as measured in number of nodes, was also of major importance in well watered plants, the relationship being logarithmic. However, during water stress or low nitrogen nutrition, proportionally more 14C moved to the roots. Furthermore, if plants were stressed slowly, the lower bolls received a greater share of the label than in well watered plants. Analysis of the distribution patterns indicated that empirical regression coefficients considering both phyllotaxis (angle) and distance between source and sink may be of use in simulations of plant performance. Using these regression coefficients and leaf photosynthesis data collected elsewhere, the distribution of total carbon within the cotton plant was calculated.