Endo-β-Mannanase Activity from Individual Tomato Endosperm Caps and Radicle Tips in Relation to Germination Rates

Abstract

~ ~ ~~Endo-P-mannanase is hypothesized to be a rate-limiting enzyme in endosperm weakening, which is a prerequisite for radicle emergente from tomato (Lycopersicon esculentum Mill.) seeds. Using a sensitive, single-seed assay, we have measured mannanase activity diffusing from excised tomato endosperm caps following treatments that alter the rate or percentage of radicle emergence. Most striking was the 100-to more than 10,000-fold range of mannanase activity detected among individual seeds of highly inbred tomato lines, which would not be detected in pooled samples. In some cases a threshold-type relationship between mannanase 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 enhanced. Partially dormant seed lots displayed a bimodal distribution of activity, with low activity apparently associated with dormant seeds in the population. Gibberellin-and abscisic acid-deficient mutant seeds exhibited a wide range of mannanase activity, consistent with their variation in hormonal sensitivity. Although the presence of mannanase activity in the endosperm cap is consistently associated with radicle emergence, it is not the sole or limiting factor under all conditions.Even though tomato (Lycopersicon esculentum Mill.) is self-pollinating and cultivars are highly homozygous genetically, germination behavior varies considerably among individual seeds. We have developed a population-based hydrotime model that accurately describes germination time courses in response to environmental and hormonal factors (Bradford, 1990(Bradford, , 1995(Bradford, , 1996 Bradford, 1990, 1994; Bradford, 1992, 1993). This model is based on the assumption that individual seeds vary in their sensitivity to these factors and particularly in the sensitivity of radicle emergence to +. If the +, , is higher (more positive) than the actual seed +, radicle emergence will not occur. The lower (more negative) the & for radicle emergente relative to the ambient +, the more rapid germination will be. The distribution of Ic., values within the seed population therefore determines both the rate and final percentage of germination. Environmental and hormonal fac- (Ni and Bradford, 1993;Dutta and Bradford, 1994;Bradford, 1995Bradford, , 1996.The population-based hydrotime model can quantify and describe seed germination patterns, but it does not identify the physiological or biochemical basis of +, , .

A Gel Diffusion Assay for Quantification of Pectin Methylesterase Activity

“…Additionally, there was an almost 10-fold difference in enzyme activity among individual seeds. Large variation in enzyme activity has been noted previously for endo-␤-mannanase in tomato seeds (39,40).…”

“…The endosperm cap was sliced from the seed and the radicle tip teased from it. Each tissue piece (endosperm cap, radicle tip, and the rest of the seed) from each seed was placed in 20 l of buffer (0.1 M citrate/ 0.2 M sodium phosphate, dibasic, pH 7.0) in a microtiter plate, covered with tape, and incubated at 25°C for 2 h (39,40). Ten microliters of the diffusate was loaded into a well in a gel containing 0.1% (w/v) of 90% esterified pectin (pH 6.0) and the plates incubated for 16 h at 30°C.…”

Regulation of Seed Germination in the Close Arabidopsis RelativeLepidium sativum: A Global Tissue-Specific Transcript Analysis

“…Endo-b-1,4-mannanase also accumulates in the micropylar endosperm of Solanum lycocarpum, D. ferox, and coffee and is thought to contribute to endosperm weakening (Bewley, 1997;Nonogaki et al, 2000;Toorop et al, 2000;da Silva et al, 2004;Arana et al, 2006;Pinto et al, 2007). Endo-b-1,4-mannanase enzyme activities of individual tomato micropylar endosperm caps vary at least 100-fold (Still and Bradford, 1997). Although the presence of endo-b-1,4-mannanase enzyme activity in the tomato endosperm cap is consistently associated with radicle emergence, it is not the sole or limiting factor under all conditions.…”

Single-seed oxygen consumption measurements and population-based threshold models link respiration and germination rates under diverse conditions

“…Germination of most control seeds was completed within 16 h, well before the large differences in subsequent respiration patterns occurred, which apparently reflect variation in respiration rates of lettuce seedlings. Q2 data for individual lettuce Population analysis of single-seed oxygen consumption 213 seeds/seedlings illustrate the wide physiological variation that can exist within apparently uniform seed lots (Still and Bradford, 1997). Although the PBT model matched the overall respiratory pattern of ageing lettuce seeds relatively well (Fig.…”

“…In addition, these are generally not sensitive enough to detect oxygen consumption of individual seeds, and therefore depend on measurements of pooled seed samples, which can only give average values for the entire population. Such averages are relatively insensitive measures for population parameters, and cannot reveal the underlying physiological variation among individual seeds, tissues or cells (Still and Bradford, 1997;Trewavas, 2012).…”