Influence of drought on the photosynthetic apparatus activity, senescence rate, and productivity in wheat plants

Abstract

Effects of soil drought at flowering stage on the functional state of photosynthetic apparatus and chloroplast enzymatic antioxidant defense systems in flag leaf during reproductive period, and the productivity of winter wheat plants of high-protein Natalka variety and drought-tolerant Podolyanka variety were studied in pot experiment. Until flowering and for the control plants during the entire vegetation, the soil moisture content was maintained at a level of 60—70 % of field capacity (FC). Drought treatment (soil moisture 30 % FC) was applied for 7 days covering flowering—early kernel watery ripe period (BBCH 61—71). After that, watering of plants was resumed to a control level which was maintained until the end of the growing season. The estimation of the chlorophyll and Rubisco content, the chloroplast antioxidant enzymes activity, and the net CO2 assimilation and transpiration rates was carried out on flag leaves. The measurements were taken on the third day of watering cessation (the first day the soil moisture reached 30 % FC, BBCH 61), at the end of the drought period (seventh day at 30 % FC, BBCH 71), and after watering resumed at the medium milk (BBCH 75) and late milk (BBCH 77) stages. The components of plant grain productivity were determined by weighing air-dry material at grain full ripeness. It was revealed, that drought stress during flowering inhibited CO2 assimilation and accelerated induction of senescence processes in wheat plants associated with degradation of photosynthetic apparatus and manifested in quicker ontogenetic drop in chlorophyll and Rubisco contents and loss of leaf photosynthetic activity. This exacerbated the drought impact on the plant organism so that after optimal watering return, the physiological and biochemical parameters were not restored to the values of control plants that were all time under optimal moisture supply. Stress-induced premature senescence reduced the supply of plants with assimilates and ultimately led to a decrease in their grain productivity. Impact of drought on flag leaf photosynthetic activity and especially on senescence induction were much more pronounced in the high-protein wheat variety Natalka with a genetically programmed earlier start of the nitrogen-containing compounds remobilization from leaves than in Podolyanka variety. The drought-tolerant variety Podolyanka keep ability to maintain much higher CO2 assimilation activity during drought period and to preserve photosynthetic apparatus from early induction of senescence due to likely more efficient chloroplast antioxidant defense systems, thereby gaining a better assimilates supply for yield formation.