Senescence in Field‐grown Wheat1

Abstract

We examined the senescence pattern of hard red spring wheat (Triticum aestivum L. em Thell) grown in a field environment. The upper five leaf blades and sheaths of the canopy were analyzed for chlorophyll, chlorophyll a/b ratio, protein, and free amino acids. An estimation of the photosynthetic activity of these organs was made by measuring the uptake of 14CO2. The photosynthetic activity of the canopy reached a maximum after anthesis, then declined rapidly thereafter. Lamina chlorophyll content reached a maximum at the time of full expansion and declined continuously thereafter. Sheath chloropyll followed a different pattern of accumulation and degradation than that of the lamina and declined more slowly than the lamina chlorophyll content. Chlorophyll a/b ratio of the leaf blades was found to vary with the position in the canopy, with lower blades having a declining a/b ratio and the upper leaves a constant ratio. The sheaths had a constant a/b ratio. Protein content of the leaf blades was highest at full expansion and decreased with age. Sheath protein was essentially constant over the season. Free amino acids content of both the lamina and sheaths showed a dramatic increase prior to anthesis, then declined thereafter. None of the components measured correlated well with the photosynthetic activity of the canopy. For this reason they were judged to be unacceptable as screening techniques for leaf senescence.