Effects of pressure on germination of seeds of wheat (Triticum aestivum cv. Barqai) in saline and in non‐saline media

Abstract

The effects of an increase in the absolute environmental pressure (air, N2, O2 or hydrostatic), up to 1 MPa, on the germination of wheat seeds and the survival of wheat seedlings were studied. Seeds were exposed to saline and non‐saline media, in Petri dishes, on a double layer of filter paper. They were then introduced for different time periods into a pressure chamber and pressurized by the addition of N2 to the chamber in the range of ambient to 1 MPa. Subsequently the seeds were left to germinate under normal atmospheric conditions. Seed germination and subsequent growth decreased during the first 6 h and then regained the control levels. Nevertheless, application of similar pressures to seeds which had been submerged under water was highly inhibitory. Such effects of pressure seem to be the result of flooding with water of some crucial intercellular spaces and a consequent disturbance of O2 supply to the germinating embryo. The additional flood‐water comprised only 1–3% of the total water content of 24‐h‐old seedlings. Sensitivity of the submerged seeds and the germinating seedlings to pressure varied with age and developmental stage. Highest sensitivity to pressure was obtained with 12 to 72‐h‐old submerged seedlings. Removal of the excess water after the pressure treatment restored the germinability of the seeds.

Effects of flooding under hydrostatic pressure on the respiratory metabolism of germinated wheat seeds

“…Such a process occurred in pressurized germinated seeds, in spite of the fact that they were transferred to a normal aerobic environment after the pressure treatment. Apparently, a short increase of hydrostatic pressure around submerged seeds, causes flooding of some crucial intercellular spaces and consequently limits the O2 supply to the cells of the germinated embryos (Malki and Waisel 1987). The inability of the embryo cells to obtain enough O, due to the flooding of their intercellular spaces with water continues for at least 48 h. Thus, the intercellular spaces play an important role in plant metabolism during seed germination by enabling free diffusion of O, to the various cells of the embryo.…”

“…If hydrostatic pressure decreases O, uptake by inrestotes their germinability (Malki and Waisel 1987).…”

“…creasing the resistance to O, diffusion due to flooding of Former studies of flooding damage to germinated intercellular spaces (Malki and Waisel 1987), then presseeds of various species have shown that the level of surized seeds should reflect anaerobiosis by a high ethadamage is positively correlated with ethanol accumu-nol production. This hypothesis is investigated in the lation (Crawford 1977, Woodstock andTaylorson 1981, present article.…”

Response of seedlings of radish (Raphanus sativus) to osmotic shock and external hydrostatic pressure

“…Nevertheless, external hydrostatic pressure, administered by means of gas pressure,, has been shown to injure plants (see Levitt 1980 and references therein). The appearance with time of a secondary stress in terrestrial plants after gas pressurization in a submerged situation (our experimental condition) has been reported; the stress derives from oxygen deficiency due to waterlogging of the intercellular spaces and the onset of fermentative metabolism with accumulation of toxic ethanol; the damage appears also in germinating seeds (Malki andWaisel 1987, Malki et al, 1989),…”

“…When the external hydrostatic pressures did not diminish the inhibition of protein, RNA and DNA syntheses, there was an inhibition of the uptake of labelled precursors, suggesting that the lack of effect might be due to a diminished availability of precursors. The hydrostatic pressure shock inhibited phosphorylation capability (Tah, 2); the effect could conceivably be linked to oxygen deficiency caused by flooding of the intercellular spaces (Malki and Waisel 1987), Recovery of protein synthesis, induced by external hydrostatic pressure, took place even if the energy charge was lower (Tabs 2 and 3), Dhindsa and Cleland (1975) reported that, in Averta coleoptiles, hydrostatic pressure was only partially able to eliminate the inhibition of protein synthesis activity by osmotic stress, and pointed out that this led to the production of qualitatively different proteins. Their results might reflect differences in O; availability in the medium under the different conditions used by these authors, inducing lack or excess of O, at the tissue level, with incomplete recovery of the process of protein synthesis and adaptive changes in the quality of the proteins synthesized.…”