Photosynthesis in different parts of a wheat plant

Photosynthetic capacity in non-leaf parts of a wheat plant and the contributions to grain yield cannot be neglected. It is important to understand the photosynthetic functions in these non-leaf organs of a crop plant. In the present research, with wheat leaves at different positions, spike, peduncle and leaf sheath as measurement materials, mathematic approaches were adopted to the analyses of photosynthetic light-response curve, photosynthetic hysteresis and the excised leaf photosynthetic declining curve. Large quantity of net photosynthesis was also measured in spike, leaf sheath and peduncle. Photosynthetic activities were higher in upper leaves than in the lower ones. The lower leaves showed a larger hysteresis than the flag leaf because of the more developed senescence and less sensitive stomatal response in the lower leaves. The higher photosynthetic hysteresis in spike, peduncle and leaf sheath might be attributed more to the morphological differences instead to an inactive photosynthetic mechanism. The response curves of photosynthesis in excised leaves to dehydration suggested that retention abilities of tissue water and photosynthesis were higher and the stomatal and cuticular transpiration in spike, peduncle and leaf sheath was lower than in leaf blades and in the flag leaf lower than in the lower leaf. It was concluded that photosynthesis in the spike possesses higher tolerance or avoidance against dehydration compared with the leaf blade and so does for the flag leaf compared with the lower leaf.