The effects on ageing and low temperature pre-sowing treatments on the membrane status and germination performance of tomato seeds

Abstract

Loss of viability and decreases in germination rate appear to be due to two independent causes during artificial ageing in tomato (Lycopersicon esculenturn Mill) seeds. only the second category of physiological damage is reversible: a low temperature presowing treatment (LTPST) capable of greatly increasing gennination rate of unaged and aged seeds had no effect on gennination capacity. Leakage of ionic solutes from seeds did not increase following ageing, but there were increased losses of small organic molecules which LTPST did not reduce. Total protein levels were unaffected during ageing and LTPST, but changes occurred during germination. Controlled deterioration caused a progressive decline in total seed phospholipid (PL) content mainly due to losses of phosphotidylcholine (:EC):losses irreversible by LTPST. Following 72 h imbibition, there was a significant increase in total PL present in untreated and treated unaged seeds and significant changes in composition of the PL fraction. LTPST had no significant effect on PL composition of viable artificially aged and unaged seeds, indicating that viability losses accanpanying controlled deterioration are related to losses of PC, but decreases in gennination rate are not. Total PL fatty acid (FA} content increased significantly following LTPST and also following 24 h ageing. Losses of total FA's between 24 hand one week's ageing occurred and were more marked in pre-treated seeds. Antioxidants prevented the viability loss usually caused by one weeks ageing and sane but not all of the FA changes. Non-viable aged seeds were unable to activate the free radical scavenging enzyme superoxide dismutase (SOD) during imbibition unlike aged and nonlethally aged seeds. LTPST had no apparent effect on SOO levels. LTPST had the same promotory effect on germination rate of naturally aged seeds as it did on artificially aged ones. Similarly germination percentage was unaffected. Phospholipid changes occurring during a period of natural ageing of up to 17 years were similar to those during artificial ageing.