Response to osmotic medium and fusicoccin by seeds of radish (Raphanus sativus) in the early phase of germination

Abstract

The effect of increasing osmotic values of the medium (mannitol) on the growth and the response mechanisms of seeds of radish (Raphanus sativus L., cv. Ton do Rosso Quarantino) during the early phase of germination was investigated in the presence or absence of fusicoccin (FC). Decreasing the water potential in the medium inhibited the growth and the evolution of protein synthesis and enhanced H+ extrusion, net uptake of K+ and malic acid synthesis. FC, which stimulates these latter functions, counteracted the inhibitory effect of the decreasing water potential of the medium on growth and protein synthesis. Neither in the absence nor in the presence of FC did decreasing water potential of the medium enhance the synthesis of soluble sugars and amino acids to support the osmotic pressure of the seeds. The osmotic and water potentials of the seeds increased during germination. FC made the increase more rapid, while mannitol kept both potentials low. The pressure potentials of the seeds also decreased with time, and both FC and mannitol enhanced this change. If the seeds were without turgor, the development of protein synthesis was blocked. The seeds counteract the effect of decreasing water potentials in the medium by: a) enhancing H+ extrusion (and, as a consequence, wall loosening and transport mechanisms) and the synthesis of malic acid as apparent in the presence of FC; b) regulating the osmotic potentials of the cells (with a lower dilution of the osmotic compounds present in the seeds due to the diminished uptake of water); c) controlling the growth through the effects of a) and b) on the pressure potentials (internal hydrostatic pressure) of the seeds and on protein synthesis.

Effects of Fusicoccin on the Early Stages of Sorghum Growth at High NaCl Concentrations

“…It can be suggested that some complementary factors are necessary for the manifestation of the FC effect. Thus, it was shown that there was a synergism in the stimulating effects of an osmoticum and FC on the proton efflux from the pea internode segments [19], in the Arabidopsis suspension culture [20], as well as during the germination of radish seeds [12]. The above points suggest that osmotic factors, such as high salt concentrations, initiate the manifestation of FC effect; under salt stress, FC affects the ionic balance, and, in particular, increases the ä + / Na + ratio [5].…”

“…Such increase could proceed due to a decrease in the rate of potassium ion efflux, which usually are rapidly secreted in the medium during the first hours of imbibition [12]. An increased potassium content in cells results in an increase in their osmotic potential providing for intense water absorption.…”

“…A protective effect of FC was observed during the germination of seeds of lettuce, cotton, rice, and Allenrolfea occidentalis under salinity [8][9][10][11]. It was also shown that, at high concentrations of mannitol, FC stimulated the imbibition of radish seeds [12]. However, in germinating seeds, the mechanisms of FCinduced physiological processes stimulating growth under high salt concentrations, remain little investigated.…”

Changes in the potato (Solanum tuberosum L.) tuber at the onset of dormancy and during storage at 23°C and 3°C. I. Biochemical and physiological parameters

“…Glucose-6-P was determined by measuring NADP § reduction at 340 nm and 25 ~ as described previously (Cocucci et al, 1990). Reducing sugars were measured by the colorimetric method of Nelson (1944).…”

Effects of Dormancy Regulating Chemicals on Innate and Salinity Induced Dormancy in the Invasive Prosopis juliflora (Sw.) DC. Shrub

“…Fusicoccin significantly alleviated the salinity-induced germination inhibition in Sporobolus arabicus (Khan and Ungar 2001c), Zygophyllum qatarense (Ismail 1990), but had no effect at higher salinity in Salicornia rubra , Aeluropus lagopoides and Urochondra setulosa (Gulzar and Khan 2002). Cocucci et al (1990) indicated that fusicoccin counteracted the inhibitory effect of a declining water potential in the medium of radish seeds by enhancing H + extrusion and synthesis of malic acid. Fusicoccin has also been shown to affect seed germination by accelerating development and by replacing the requirements for light and endogenous hormones in breaking dormancy (Lado et al 1975).…”