Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Abstract

Decoated pepper (Capsicum annuum L. cv Early Calwonder) seeds germinated earlier at 25°C, but not at 15°C, compared to coated seeds.The seed coat did not appear to impose a mechanical restriction on pepper seed germination. Scarification of the endosperm material directly in front of the radicle reduced the time to germination at both 15°C and 25°C.The amount of mechanical resistance imposed by the endosperm on radicle emergence before germination was measured using the Instron Universal Testing Machine. Endosperm strength decreased as imbibition time increased. The puncture force decreased faster when seeds were imbibed at 25°C than at 15°C. The reduction in puncture force corresponded with the ability of pepper seeds to germinate. Most radicle emergence occurred at 15°C and 25°C after the puncture force was reduced to between 0.3 and 0.4 newtons. Application of gibberellic acid4+7 (100 microliters per liter) resulted in earlier germination at 15°C and 25°C and decreased endosperm strength sooner than in untreated seeds. Similarly, high 02 concentrations had similar effects on germination earliness and endosperm strength decline as did gibberellic acid4+7, but only at 25°C. At 15°C, high 02 concentrations slowed germination and endosperm strength decline.found that, by increasing the growth rate of the embryo, this restriction could be overcome. Red light induced growth in the lettuce embryo, enabling it to grow through the endosperm. Pavlista and Haber (10) proposed that both the mechanical force of the growing embryo pushing against the endosperm, and the enzymic weakening of the endosperm were necessary for lettuce seed germination. They observed that when weakening of the endosperm was inhibited, the embryos grew and buckled in the endosperm encasing but did not germinate.Jones (6) determined that the cell walls of lettuce endosperm were increasingly degraded with longer incubation times, and following germination the walls were extensively broken down. Tao and Khan (12) determined that endosperm strength did not appear to be directly related to radicle protrusion in lettuce seed. Halmer et al. (4) reported that enzymic degradation of a mannosecontaining polysaccharide in lettuce endosperm cell walls was by red light or gibberellin. Enzymic activity increased markedly only after radicle emergence and thus did not correspond with the movement of the radicle through the endosperm.Pepper embryos are surrounded by endosperm materials which make up the bulk of food reserves for the embryo and young seedling (2). The experiments which follow test the mechanical resistance of the seed coat and endosperm during germination of Capsicum annuum at optimal and suboptimal temperatures.Seed coats and surrounding structures may influence the ability of a seed to germinate through interference with water uptake, gas exchange, diffusion of endogenous inhibitors, or by mechanical restriction of embryo growth (5, 8). In seeds that do not have hard seed coats or require scarification for water uptake, other seed parts ...

Carboxymethylcellulase Activity in Lettuce Seeds Prior to Germination

“…A similar study on osmotic pressure and on mechanical strength of the endosperm on tomato seeds came to the same conclusion [19] [20]. This was also concluded from studies on cress [21] and pepper [22]. Light and gibberellins may affect both endosperm weakening and embryo expansion while external osmotic pressures may inhibit only the latter.…”

A Water Relations Analysis of Seed Germination Rates

“…In many seeds, the embryo is surrounded by endosperm, perisperm, or other tissues that may restrict radicle growth (8,12,(28)(29)(30). A satisfactory model of seed germination rates should be able to account for, and quantitate, the influence of such enveloping tissues.…”

Seed Germination-The Biochemical and Molecular Mechanisms

“…Since the testa is a dead tissue in the mature seeds of Arabidopsis and most (if not all) species, physiological changes are expected to occur in the living endosperm. Endosperm weakening is a well known phenomenon in the seeds of other plant species such as lettuce (Halmer et al 1975), pepper (Watkins and Cantliffe 1983), tomato (Groot and Karssen 1987, Nonogaki et al 1992, 1998a, 1998b, tobacco (LeubnerMetzger et al 1996) and Datura (Sánchez and de Miguel 1997). Since the endosperm of Arabidopsis consists of only a single cell layer, it is less likely that endosperm weakening plays a decisive role in seed germination in Arabidopsis.…”

“…Alternatively, cell wall loosening in the embryonic axis, which causes cell elongation, might increase the embryo growth potential (Carpita et al 1979a, 1979b, Nonogaki et al 1998a). The endosperm cell walls are known to be weakened by enzymatic degradation of polysaccharides which are an important component of the thick cell walls (Halmer et al 1975, Watkins and Cantliffe 1983, Groot et al 1988, Nonogaki et al 1992, 1998b. The embryoendosperm balance theory including hormonal control will be re-visited in the last section.…”