Effect of Temperature on the Short Chain Fatty Acid-induced Inhibition of Lettuce Seed Germination

Abstract

In lettuce, Lactuca sativa short chain fatty acids (C6 -Co) vary in their effectiveness as inhibitors of germination according to temperature; the higher the temperature, the greater the inhibition. A linear relationship exists between temperature and the dose causing half-maximal germination. Nonanoic (C9) acid is the most effective.When extrapolated to the abscissa, really zero concentration of acid, the regression lines intercept at 36.8 C ± 2.6 C. It may be that at this temperature the whole membrane becomes fluid without acid being present but with acid there was complete fluidizing at lower temperatures the degree of fluidity being determined by the amount and type of acid present.This speculation distinguishes between the fluidizing of the bulk lipids and the character of the lipid layer that may be around certain key membrane proteins.Lettuce seed germination is dependent on temperature, there being a value above which there is a requirement for light. The need for this light requirement can be overcome if the seed is treated with GA (4) and/or cytokinin (3). On the other hand the temperature at which the seed becomes light-sensitive can be lowered if they are exposed to coumarin (9) and possibly ABA (5).Short chain length fatty acids (chain length C6 -C12) are known to inhibit seed germination, and in the case of lettuce to impose a light requirement (1).Inasmuch as these fatty acids might be expected to affect lipid membranes, their action might vary according to the temperature of application. With an increasing level of low mol wt acid incorporated into the lipid membrane it could be predicted that there would be a change in the temperature at which the membrane undergoes a change in its functional characteristics.It was this hypothesis that we tested. MATERIALS AND METHODSA batch of lettuce seed (Lactuca sativa L. cv. Grand Rapids) which became light-requiring at high temperatures was obtained from the Page Seed Co., Greene, N.Y. (Batch No. 014576). At 30 C the germination was less than 1%, at 20 C 16%, and when treated with red light, 369 mJ cm2, the germination rose to 8 and 90%1o, respectively.Seeds were counted into batches of 50 prior to dispensing over a 4.25-cm Whatman No. 3 filter paper lining a 4.5-cm Petri dish base. These seed lots were held at -20 C until required. Prior to dispensing the seed the filter paper was loaded with an amount of acid in ether that would give the desired molar concentration when 1.5 ml of H20 were added after the ether had evaporated. Zero concentration of acid (control) was treated with solvent. A 61 range of concentrations was chosen to encompass the sharp transition from zero effect to maximum effect of each acid and a number of temperatures from 12 to 28 C selected. The temperatures were held to better than ± 1 C.In this experiment the seeds were irradiated 2 hr after the start with red light (656 nm, band width 10 nm) obtained by filtering the emitted radiation from a 12-v 100-w quartz halogen lamp through 20 cm of H20 and an interference filter (Ba...

Role of Endogenous Growth Regulators in Seed Dormancy of Avena fatua

“…Whereas most hormone responses are proportional to the logarithm of the concentration, the inhibition of germination by NA exhibited a threshold effect. Similarly shaped dose-response curves have been reported for the inhibition of germination of seeds in other species by short chain fatty acids (23,24).…”

“…Stewart and Berrie (23) reported that the transition between germinability and nongerminability in lettuce seeds with increasing concentration of short chain fatty acids was essentially linear. This implied that, during the course of determining the doseresponse relationship between short chain fatty acid concentration and the inhibition of seed germination, several concentrations were found that caused varying degrees of inhibition.…”

Effects of Temperature, Water Potential, and Light on Germination Responses of Redroot Pigweed Seeds to Ethylene

“…This apparent narrowing of the population distribution with regard to ethylene sensitivity may reflect changes in cellular and organelle membrane characteristics. Membrane phenomena have been implicated in seed germination responses to temperature (13,28), light (14,32) and ethylene (18), and Hendricks and Taylorson (14) reported a membrane phase shift at 32 C in dormant redroot pigweed seeds.…”

“…A few flasks of seeds were also incubated at -10 and -12 bars, and 5.1 and 51,ul/l ethylene, to determine whether the gas can cause some germination under such severe stress. We also examined the ethylene-water potential interaction in continuous white light (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30),tE/m2. s).…”

Ectopic expression of WRI1 affects fatty acid homeostasis in Brachypodium distachyon vegetative tissues

“…Thus, overaccumulation of free FAs is expected to be detrimental to tissues. For example, exogenous and endogenous FAs are known to inhibit coleoptile elongation of oat (Avena fatua; Ando and Tsukamotoa, 1981;Ohkawa and Nishikawa, 1987), longitudinal cell growth of Arabidopsis (Li et al, 2011), axillary bud growth of tobacco (Tso, 1964), seedling growth of rice (Oryza sativa; Tsuzuki et al, 1987), and germination of lettuce (Lactuca sativa), oat, and mustard (Sinapsis alba; Le Poidevin, 1965;Stewart and Berrie, 1979;Metzger and Sebesta, 1982). Furthermore, the accumulation of unsaturated FAs has been linked to cell death.…”