Effects of Gibberellin, Kinetin, Thiourea, and Photomorphogenic Radiation on Mitotic Activity in Dormant Lettuce Seed

Abstract

Lettuce seed germination can be stimulated, probably by distinct mechanisms, by any of the three widely studied morphogenic agents: gibberellin, kinetin, or red light (11). It has been shown that cellular expansion is both necessary and sufficient and that cell division is neither necessary nor sufficient for the initiation of lettuce seed germination (8 The criterion of germination was visual detection of radicle protrusion. Radicles (1-2 mm) from nongerminated seeds were excised and prepared as described previously (8). The apical 0.5 mm was examined for mitotic activity. An entire dish of seeds was sampled at one time for germination percentages and mitotic activity in nongerminated seeds. Once sampled, the dish was removed from the experiment.Respiratory rates were determined by placing 50 seeds in 1.2 ml of solution in the main compartment of Warburg flasks. We placed 0.2 ml of 20 % KOH and a fluted piece of filter paper in the center well to measure oxygen consumption by the direct method (32).The term "germination" is used here in the physio-

Effects of Light and Growth Regulators on Germination and Radicle Growth of Lettuce Seeds Held Under High‐temperature Stress and Water Stress

“…However, at 30 °C most seeds underwent cell division but did not germinate, and in seeds held in mannitol solution at 26 °C cell division preceded cell expansion by many days. Haber and Luippold (1960b) also considered that dormancy of this type, which is not generally related either to a significant depression of overall metabolism or to prevention of cell division, is a subtle block that specifically prevents the initiation of cellular expansion.…”

“…There are many theories on the precise mode of action of light and growth regulators in breaking seed dormancy, especially in lettuce (Haber and Luippold, 1960b;Ikuma and Thimann, 1963b;Scheibe and Lang, 1965;Lewak and Khan, 1977). The mechanism of phytochrome action is rapid and involves changes at the biophysical level of the cell, such as changes in the properties of membranes (Kendrick, 1976), and in lettuce seeds held in PEG solution phytochrome stimulation has been shown to result in a decrease of solute potential within the axes (Carpita and Nabors, 1977).…”

Effects of Indoleacetic Acid on Growth Without Mitosis & on Mitotic Activity in Absence of Growth by Expansion

“…Thus, for example, a primary action of a growth-regulator on growth by expansion can secondarily affect mitotic activity (14). Conversely, a primary action of a growthregulating agent on cell division can secondarily affect over-all growth by expansion (11).…”

“…The high concentration (2 X 10-3 M) of IAA thus had four deleterious effects on lettuce seeds: A: decreased mitotic activity (in the absence of added Radicles with mitotic figures** 3(1),1 (3),1 (7) 1 (1) 10 (1) ,5 (2),2 (3),2 (4) 3 (5) ,1 (7) ,1 (8) ,l (11 ), 1 (14) ,1 (21 ),1 (24) ,1 (31 ) 1 (1),1 (2),4(4),1 (7), 1 (8),1 (10) ,1 (17),1 (25), 1 (27) To complement the studies just described, on mitotic activity without growth by expansion, we studied IAA effects on gamma-plantlets. When roots, coleorhizae, and epiblasts in these seedlings grown from gamma-irradiated (800 kr) grain, were germinated in 10-I of 10 51 IAA, they were found to lack DNA synthesis and mitosis by the same criteria used in earlier studies in which the gamma-plantlets were germinated and grown in water (11,12).…”

“…in the absence of over-all growth by expansion (viz., dormant lettuce seeds, [13][14][15], and B: growth and differentiation without significant deoxyribonucleic acid (DNA) synthesis, mitosis, and cell division (viz., wheat grown from gamma-irradiated grain, 9, 11). In this paper we report the effects of IAA on these two systems, with particular reference to interactions of IAA with kinetin on cell division (29), and we suggest how such effects might underlie various actions of auxin as a regulator of normal growth.…”