Efficacy of treatments for delaying senescence of wheat leaves: I. Senescence under controlled conditions

Senescence of wheat (Triticum aestivum L,) leaves is accelerated by high temperature during the critical grain filling period. Loss of Leaf viability decreases grain yields and the response to production inputs. Studies were conducted under controlled conditions to identify treatments that might delay the rapid senescence induced by high temperature. Shoots of 30-d-old seedlings of 'Nesma' wheat were immersed in 0.1 mill solutions of kinetin, abscisic acid, or one of six mineral salts [0.1 mM Ca(NO3)(2), NaH2O4, K2SO4, KH2PO4, KNO3, or NH4H2PO4] and incubated at 20 and 30 degrees C with continuous irradiance of 150 mu mol m(-2) s(-1). Chlorophyll and free amino acid concentrations and crude protease enzyme activity were monitored over an 8-d period as measures of shoot senescence. High temperature and abscisic acid generally increased all senescence processes, whereas kinetin and several mineral salts reduced the loss of chlorophyll and slow-ed the increases in amino acid concentration and protease activity compared with amounts in shoots incubated in distilled water, Mineral salts that contained N or P were usually most effective, particularly in countering rapid senescence at 30 degrees C relative to 20 degrees C. We conclude that senescence processes induced by high temperatures in detached shoots resemble those in whole plants and that the feasibility of delaying senescence by foliar application of selected compounds under field conditions merits investigation.