The Effect of Low Temperature Pre-Sowing Treatment on the Germination Performance and Membrane Integrity of Artificially Aged Tomato Seeds

Loss of seed viability and decrease in germination rate appearto be due to two independent sets of events occurring duringartificial ageing in tomato (Lycopersicon esculentum Mill) seeds.Only the second category of physiological damage is reversible:a low temperature pre-sowing treatment being capable of greatlyreducing the time to fifty percent germination of both unagedand aged seeds, but having no effect on germination capacity.Leakage of ionic solutes from the seeds did not increase followingageing, but there were considerable increases in losses of smallorganic molecules. Low temperature pretreatments did not reducethe rate of loss of either amino acids or reducing sugars fromaged seeds. The implications of the use of artificial ageingin combination with low temperature pre-sowing treatments inthe study of small seed physiology is discussed, as is the valueof solute leakage studies in this kind of seed. Key words: Tomato seeds, Accelerated ageing, Seed treatment, Membranes     

Studies on the Changes in the Major Nucleic Acid Components of Tomato Seeds (Lycopersicon esculentum Mill.) Resulting from Osmotic Presowing Treatment

Extensive accumulation of nucleic acid may be one of the factorsinvolved in the acceleration of tomato seed germination by osmoticpresowing treatment. The experiments reported here were designedto characterize the changes in the major nucleic acids duringosmotic pretreatment and subsequent germination. Polyacrylamidegel electrophoresis showed that ribosomal RNA comprised themajor part of this net synthesis, but it was more difficultto ascertain whether or not there was a proportional increasein sRNA, as part of the latter peak may comprise comigratingfragments of degraded rRNA. The mass ratio of 25S: 18S rRNAsextracted from dry seeds was near unity, while during normalgermination and during pretreatment this ratio increased toabout 1?9:I, close to the theoretical ratio assuming 25S and18S rRNAs occur in equimolar proportions. This leads to thespeculation that replacement of old ribosomes may occur duringearly germination and pretreatment, although this would notaccount for all the synthetic activity observed during the latterprocess. Use of the diphenylamine colour reaction showed that no increasein DNA results from pretreatment and that the onset of the firstS-phase during subsequent germination of pretreated seeds wascommensurate with the advancement of the time to 50% germination.     

Changes in Nucleic Acid Levels Associated with Improved Germination Performance of Tomato Seeds After Low Temperature Presowing Treatment

Low temperature presowing treatment (LTPST) of tomato seeds,var. Moneymaker, increases their rate of germination. Duringthis treatment there is a large increase in nucleic acid content,especially rRNA, within the seeds. Denaturing gel electrophoresisindicates that the quality of this RNA improves during LTPST.Although replacement of fragmented rRNA may be an importantprerequisite for successful germination, the data show thatthis is unlikely to be the immediate cause of more rapid seedgermination. When compared with untreated controls during subsequentgermination, treated seeds show reduced rates of nucleic acidaccumulation and reduced RNA polymerase activity per unit DNA,implying that rRNA synthesis within these seeds is under somemeasure of stringent control. The association between nucleicacid metabolism and germination is discussed. tomato, Lycopersicon esculentum Mill., seed germination, presowing treatment, RNA, RNA polymerase     

A Comparison of Changes in the Germination Responses and Phospholipid Composition of Naturally and Artificially Aged Tomato Seeds

The changes in germinability and phospholipid content of naturallyand artificially aged tomato seeds, variety Kingley Cross, werecompared. Subsequent low temperature pre-sowing treatment (LTPST)was unable to prevent decreases in the germination capacityof aged samples, but significantly improved germination rates.However, in contrast to previous studies on artificial ageingusing the variety Moneymaker, losses of total phospholipid werenot always well correlated with decreased germinability. Totalphospholipid levels in naturally aged seeds were largely unaffectedby pre-sowing treatment, but the proportion of phosphatidylcholinewas greatly increased. These results strongly suggest that lossesof phospholipid are coincidental rather than causative eventsin the loss of seed viability during ageing, and that the patternof changes depends on the type of ageing experienced by theseeds. Controlled deterioration, seed ageing, tomato seeds, seed treatment, phospholipids     

An evaluation of the potential of low temperature pre-sowing treatments of tomato seeds as a means of improving germination performance

Low temperature pre-sowing treatment of tomato seeds substantially enhanced germination rates and was much more effective at improving uniformity of germination than equivalent osmotic treatments. Although radicle emergence was inhibited by the low temperature, imbibition studies showed that seeds were maintained at lag-phase moisture contents during treatment and some aspects of germinative metabolism began. No evidence was found for improved seedling growth rates per se as a result of pretreatment: in fact, initial axis growth may be temporarily reduced, probably as a consequence of depletion of reserves during the treatment period.