Seeds of tomato (Lycopersicon esculentum Mill.) which develop in a fully hydrated environment in the fruit switch from a developmental to a germinative mode without a requirement for desiccation

Abstract

Seed water content is high during early development of tomato seeds (10-30 d after pollination (DAP)), declines at 35 DAP, then increases slightly during fruit ripening (following 50 DAP). The seed does not undergo maturation drying. Protein content during seed development peaks at 35 DAP in the embryo, while in the endosperm it exhibits a triphasic accumulation pattern. Peaks in endosperm protein deposition correspond to changes in endosperm morphology (i.e. formation of the hard endosperm) and are largely the consequence of increases in storage proteins. Storage-protein deposition commences at 20 DAP in the embryo and endosperm; both tissues accumulate identical proteins. Embryo maturation is complete by 40 DAP, when maximum embryo protein content, size and seed dry weight are attained. Seeds are tolerant of premature drying (fast and slow drying) from 40 DAP.Thirty-and 35-DAP seeds when removed from the fruit tissue and imbibed on water, complete germination by 120 h after isolation. Only seeds which have developed to 35 DAP produce viable seedlings. The inability of isolated 30-DAP seed to form viable seedlings appears to be related to a lack of stored nutrients, since the germinability of excised embryos (20 DAP and onwards) placed on Murashige and Skoog (1962, Physiol. Plant. 15, 473-497) medium is high. The switch from a developmental to germinative mode in the excised 30- and 35-DAP imbibed seeds is reflected in the pattern of in-vivo protein synthesis. Developmental and germinative proteins are present in the embryo and endosperm of the 30- and 35-DAP seeds 12 h after their isolation from the fruit. The mature seed (60 DAP) exhibits germinative protein synthesis from the earliest time of imbibition. The fruit environment prevents precocious germination of developing seeds, since the switch from development to germination requires only their removal from the fruit tissue.

A Role for the Surrounding Fruit Tissues in Preventing the Germination of Tomato (Lycopersicon esculentum) Seeds

“…Seeds isolated at 40 DAP germinate to a greater percentage (approximately 95%) than those isolated at 35 DAP (65%) (3), and yet the ABA concentration of the embryo (and seed) is higher in the former (Fig. 1).…”

“…Throughout development, tomato seeds are embedded in locular tissue derived from the pericarp (24 (3). Sheath ABA concentration is much lower than that of the locular tissue early in development, but by 30 DAP there is no difference between the two, and after 40 DAP, sheath ABA is appreciably higher (Fig.…”

“…Maturation drying or partial drying of seeds is proposed to be the signal for the seed that removes the influence of the maternal environment on seed development (15). Tomato seeds usually do not undergo maturation drying, and the mature tomato seed has a water content of 40% (3). A high seed water content in the mature seed appears to be a characteristic of fleshy fruits (20,21,26).…”

“…A high seed water content in the mature seed appears to be a characteristic of fleshy fruits (20,21,26). Throughout development, tomato seeds are embedded in locular tissue, which has a water content ranging between 92 and 98% (3).…”

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

“…When seeds are removed from the fruit after the mid-point of their development, however, they complete germination prematurely on water without the requirement for a maturation-or premature-desiccation phase (Berry and Bewley 1991), although they are tolerant of drying. Synthesis of storage proteins is a useful marker of seed development, and production of these reserves ceases within hours of removal of the seed from the fruit (Berry and Bewley 1991).…”