Developing tomato seeds when removed from the fruit produce multiple forms of germinative and post-germinative endo-?-mannanase. Responses to desiccation, abscisic acid and osmoticum

Abstract

Abstract. Several isoforms of endo-l,413-D-mannanase (EC3.2.1.78) are produced in the endosperm and embryo of tomato (Lycopersicon esculentum Mill.) seed prior to the completion of germination. Other isoforms appear in the embryo and in the lateral endosperm following germination. This occurs in seeds removed from the fruit prior to completion of development at 45 d after pollination and placed directly on water, or following drying. Hence desiccation is not required to induce either germination-or post-germination-related mannanase activity. Incubating seeds in abscisic acid or osmoticum results in a reduction of both germination and total mannanase activity, but the isoforms that are produced in the embryo and micropylar region of the endosperm are identical to those produced in water-imbibed seeds prior to germination. Incubation of seeds in a high concentration of abscisic acid prevents all enzyme production. Only after the completion of germination does mannanase increase in the lateral regions of the endosperm. In contrast, mannanase is produced in the micropylar region regardless of whether the seed germinates or not. The isoforms produced in the two regions of the endosperm are different, those in the lateral endosperm being more similar to those produced in the cotyledons and axes of the embryo. Embryos and endosperms dissected prior to completion of germination and incubated separately produce far fewer isoforms than when these parts are together in the intact seed.Key words: Abscisic acid -Desiccation -Endo-[5-mannanase -Endosperm -Lycopersicon (seed germination)-Osmoticum * Present address: Botanisches Institut, der E.M. Arndt Universit~it, Grimmer Strasse 88, D-17489 Greifswald, Germany Abbreviations: ABA = cis-abscisic acid; DAP = days after pollination; GA = gibberellin; IEF = isoelectric focusing; PEG = polyethyleneglycol; pI = isoelectric point

Molecular cloning of a cDNA encoding a (1→4)-β-mannan endohydrolase from the seeds of germinated tomato ( Lycopersicon esculentum )

“…This observation must be reconciled with the multiple (1®4)-b-mannanase isoforms that have been separated from extracts of germinated tomato seed by isoelectric focussing, where up to 15 active (1®4)-b-mannanase bands are visible (Fig. 4) (Toorop et al 1996;Voigt and Bewley 1996). The obvious conclusion is that many of the isoforms present on isoelectric focussing gels are not true genetic isoenzymes, but are generated from a relatively small number of (1®4)-b-mannanases by post-translational modi®cations.…”

“…This can be compared with a value of 38 000 reported for the (1®4)-b-mannanase isoform MI puri®ed from tomato endosperm (Nonogaki and Morohashi 1996). The pI calculated from the primary structure of the enzyme is 5.3; isoelectric focussing of endosperm extracts from germinated tomato seeds revealed the presence of several isoforms with pI values in the range 5.2±5.8 (Toorop et al 1996;Voigt and Bewley 1996).…”

“…Production of the enzyme occurs in the micropylar (radicle) end of the endosperm prior to the completion of germination (Nonogaki and Morohashi 1996;Toorop et al 1996), and weakening of this tissue could be a prerequisite to permit radicle extension (Groot et al 1988;Ni and Bradford 1993;Leviatov et al 1995). Following germination, (1®4)-b-mannanases are also produced in the lateral (cotyledonary) region of the endosperm (Nonogaki and Morohashi 1996;Toorop et al 1996;; the isoforms of the enzyme produced in the lateral endosperm are dierent from those in the micropylar endosperm (Voigt and Bewley 1996).…”

An Increase in Pectin Methyl Esterase Activity Accompanies Dormancy Breakage and Germination of Yellow Cedar Seeds

“…Three enzymes contribute to the hydrolysis of the galactomannans: ␣-galactosidase, a mannohydrolase, and endo-␤-mannanase. More recent studies (focusing on endo-␤-mannanase) have revealed that only the isoforms of the enzyme that are produced during germination have a potential role in weakening the endosperm (Nonogaki and Morohashi, 1996;Toorop et al, 1996;Voigt and Bewley, 1996). Endo-␤-mannanase is also produced in the endosperm of lettuce seeds when the seeds are released from dormancy by GA or red light (Halmer et al, 1976) and seeds of Datura ferox produce endo-␤-mannanase and ␤-mannosidase in the micropylar region of the endosperm after red-light stimulation, several hours before the radicle protrudes through it (Sanchez and de Miguel, 1997).…”

Vacuolar H+-ATPase Is Expressed in Response to Gibberellin during Tomato Seed Germination

“…The physical weakening of the endosperm cap tissue to allow radicle emergence is dependent upon gibberellin (GA) (Groot and Karssen, 1987). Endosperm cap weakening is accompanied by an increase in the activity of cell wall hydrolytic enzymes, including endo-␤-mannanase (Groot et al, 1988;Nomaguchi et al, 1995;Nonogaki and Morohashi, 1996;Voigt and Bewley, 1996;Dahal et al, 1997;Nonogaki et al, 1998), cellulase (Sánchez et al, 1985;Leviatov et al, 1995), polygalacturonase (Sitrit et al, 1999), arabinosidase, ␤-1,3-glucanase, and chitinase (Bradford et al, 2000). In addition, the loss of lipid and protein bodies and cellular vacuolization occurs initially in the radicle tip and endosperm cap tissues prior to radicle emergence (Mella et al, 1995;Nonogaki et al, 1998).…”