Class I β-1,3-Glucanase and Chitinase Are Expressed in the Micropylar Endosperm of Tomato Seeds Prior to Radicle Emergence

Abstract

β-1,3-Glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) mRNAs, proteins, and enzyme activities were expressed specifically in the micropylar tissues of imbibed tomato (Lycopersicon esculentum Mill.) seeds prior to radicle emergence. RNA hybridization and immunoblotting demonstrated that both enzymes were class I basic isoforms. β-1,3-Glucanase was expressed exclusively in the endosperm cap tissue, whereas chitinase localized to both endosperm cap and radicle tip tissues. β-1,3-Glucanase and chitinase appeared in the micropylar tissues of gibberellin-deficient gib-1tomato seeds only when supplied with gibberellin. Accumulation of β-1,3-glucanase mRNA, protein and enzyme activity was reduced by 100 μM abscisic acid, which delayed or prevented radicle emergence but not endosperm cap weakening. In contrast, expression of chitinase mRNA, protein, and enzyme activity was not affected by abscisic acid. Neither of these enzymes significantly hydrolyzed isolated tomato endosperm cap cell walls. Although both β-1,3-glucanase and chitinase were expressed in tomato endosperm cap tissue prior to radicle emergence, we found no evidence that they were directly involved in cell wall modification or tissue weakening. Possible functions of these hydrolases during tomato seed germination are discussed.

Protein expression during seed development in Araucaria angustifolia: transient accumulation of class IV chitinases and arabinogalactan proteins

“…As observed in seeds of Lycopersicon esculentum (Wu et al 2001) and Cucumis melo (Witmer et al 2003), the induction of several proteins exhibiting chitinolytic activity during seed maturation is probably related to a pro-active defense strategy against pathogen attack. During seed maturation in A. angustifolia, zygotic embryos and megagametophytes accumulate water, lipids, proteins, and carbohydrates (Astarita et al 2003, Panza et al 2002 thus becoming an attractive target for microbial invasion.…”

Emerging and established model systems for endosperm weakening.

“…P↓: endosperm weakening during germination was measured as decreasing puncture force; GA↓: endosperm weakening promoted by GA; and ABA↑: endosperm weakening inhibited by ABA. Toorop et al, 2000;Wu et al, 2000) and Laminales ( Junttila, 1973;Finch-Savage and Clay, 1997). All these experiments showed a decline in the puncture force of the micropylar endosperm prior to endosperm rupture (P↓ in Fig.…”

“…Endosperm weakening of tomato is also biphasic, with a first phase that is ABA-insensitive. In this case the second phase, which is inhibited by ABA, has been reported to account for ~6% (30 mN; Wu et al, 2000) or ~24% (80 mN; Toorop et al, 2000) of the total tomato micropylar cap weakening. These results were obtained by incubating whole seeds in a medium with and without ABA, and dissecting the seeds when puncture-force measurements were performed Karssen, 1987, 1992;Toorop et al, 2000;Wu et al, 2000).…”

“…In this case the second phase, which is inhibited by ABA, has been reported to account for ~6% (30 mN; Wu et al, 2000) or ~24% (80 mN; Toorop et al, 2000) of the total tomato micropylar cap weakening. These results were obtained by incubating whole seeds in a medium with and without ABA, and dissecting the seeds when puncture-force measurements were performed Karssen, 1987, 1992;Toorop et al, 2000;Wu et al, 2000). If micro pylar caps are dissected from tomato seeds prior to the onset of endosperm weakening (3 h), a further 24 h incubation of isolated micropylar caps in medium with GA results in endosperm weakening (i.e.…”

“…Direct measurements of the effect of ABA on endosperm weakening by punctureforce experiments have been published only for the asterid species like coffee and tomato (Toorop et al, 2000;Wu et al, 2000;da Silva et al, 2004da Silva et al, , 2005. The coffee embryo is enveloped by an endosperm tissue and surrounded by an endocarp (da Silva et al, 2004).…”