ENDO-BETA-MANNANASE ACTIVITY FROM INDIVIDUAL TOMATO ENDOSPERM CAPS AND RADICLE TIPS IN RELATION TO GERMINATION RATES

Endo-beta-mannanase is hypothesized to be a rate-limiting enzyme in en dosperm weakening, which is a prerequisite for radicle emergence from tomato (Lycopersicon esculentum Mill.) seeds. Using a sensitive, singl e-seed assay, we have measured mannanase activity diffusing from excis ed tomato endosperm caps following treatments that alter the rate or p ercentage of radicle emergence. Most striking was the 100- to more tha n 10,000-fold range of mannanase activity detected among individual se eds of highly inbred tomato lines, which would not be detected in pool ed samples. In some cases a threshold-type relationship between mannan ase activity and radicle emergence was observed. However, when radicle emergence was delayed or prevented by osmoticum or abscisic acid, the initial increase in mannanase activity was unaffected or even enhance d. Partially dormant seed lots displayed a bimodal distribution of act ivity, with low activity apparently associated with dormant seeds in t he population. Gibberellin- and abscisic acid-deficient mutant seeds e xhibited a wide range of mannanase activity, consistent with their var iation in hormonal sensitivity. Although the presence of mannanase act ivity in the endosperm cap is consistently associated with radicle eme rgence, it is not the sole or limiting factor under all conditions.