Involvement of endomannanase in the control of tomato seed germination under low temperature conditions

The cause of differences in germination rates in a cold-tolerant tomato line (PI341988), a control line (UC82B), and six progeny lines stemming from crosses and backcrosses between the two parent lines was investigated. Pursuant to earlier work showing that differences in germination ability at 12°C are due to the barrier imposed by the endosperm layer, we analysed the activity of cell-wall-hydrolysing enzymes extracted from these lines. A significant increase in endomannanase activity was found in plant line PI341988 prior to germination at 12°C. Extracts of PI341988 seeds that had imbibed at either 12 or 25°C exhibited higher endomannanase activity than their counterparts from plant line UC82B. Moreover, a positive relationship was found between germination ability at low temperature and endomannanase activity in the six progeny lines. Analysis of endomannanase activity in sub-regions of the seed indicated that the increase in activity prior to germination was higher in the micropylar endosperm cap than in the rest of the seed. Exogenous application of mannanase originating from soil-borne bacteria increased germination rates under both moderate and low temperature conditions. Cellulase (endo-1, 4-β-glucanase) activity was also found to be higher in plant line PI341988. However, the activity of this enzyme probably increases after germination and it is therefore not considered as a key enzyme controlling germination at low temperatures.