LEAF DIFFUSIVE RESISTANCE, SURFACE TEMPERATURE, OSMOTIC POTENTIAL AND 14CO2-ASSIMILATION CAPABILITY AS INDICATORS OF DROUGHT INTENSITY IN RAPE

Leaf diffusive resistance, temperature and osmotic potential were evaluated in three Brassica campestris and three B. napus cultivars under both irrigated and rain-fed environments. These techniques differentiated between environments but not between cultivars within environments. Incorporation of 14CO2 by stressed plants of two cultivars under rain-fed conditions showed more promise as a means of differentiating cultivar drought response.

DISTRIBUTION OF PHOTOSYNTHATES AFTER 14CO2 ASSIMILATION BY STEMS, LEAVES, AND PODS OF RAPE PLANTS

Rape (Brassica napus L. cv. Zephyr) plants were allowed to assimilate 14CO2 through lower and upper stem internodes, leaves, and pods. Lower stem internodes exported few 14C-labelled assimilates. Lower leaves exported assimilates to the roots, whereas upper stems and leaves exported primarily to seeds and pods. Pods did not export labelled assimilates to other pods or plant parts but labelled photosynthate was detected in seed of the treated pod. The older the pod was, the greater the amount of radioactivity detected in the seed. Pods were also sinks for labelled assimilates from upper stem internodes and leaves.

PHOTOSYNTHATE TRANSLOCATION IN TILLERED ZEA MAYS FOLLOWING 14CO2 ASSIMILATION

Photosynthate translocation in field-grown corn (Zea mays L.) as influenced by tillering was studied by offering 14CO2 to a leaf blade on either the main stalk or tiller. Translocation from the labeled leaf blade of the main stalk or its tiller differed markedly depending upon stage of development at labeling and harvest. In plants assimilating 14CO2 before tasseling, little photosynthate was translocated from the labeled plant to the tiller, or conversely. When the ear leaf blade of the main plant was labeled with14CO2 4 days post-silking, the main ear and stalk were major sinks for 14C-assimilates until physiological maturity. When the tiller ear leaf blade was labeled, the tiller stalk was the major sink at first, but the tiller ear became a strong sink later. During grain filling, source-sink relationships were strongly dependent upon the presence of ears on the main plant, tiller, or both. When both had an ear, the developing ear on the labeled main plant or tiller was the major sink. When neither had an ear, the stalk of the labeled main plant or tiller was the major sink. When the labeled tiller had no ear, 14C-photosynthate was translocated to the ear on the main plant; an earless main plant also supplied the tiller ear.