This paper studied on the role of calcium in 6-BA-induced swelling of protoplasts isolated from hypocotyl in etiolated mung bean(Phaseolus radiatus L.) seedlig. Protoplasts incubated in CaCl2-bearing medium without hormone maintained a constant volume. To treat with 6-BA, they began to swell after 15 minutes, and continually swelled to the maximum volume 30 minutes later when they were treated with 10-1 mol/L 6-BA(Fig.2). However, the protoplasts could not swell when 6-BA was added into the medium without CaCl2(Fig.1). It was suggested that Ca2+ was necessary for 6-BA to induce protoplast swelling. 6-BA enabled the protoplasts to swell in less extent when K-. Zn2+, Ba2+or Mg2-instedad of Ca2-(Fig.3). Radioisotope experiments showed that K+influx incrased when Ca2+ as replaced by K+(Fig.4). Ca2+ accumulation in protoplasis treated by 6-BA was munch higher than that of control, and the time course of Ca2+ accumu-lation was similar to protoplasts swelling (Fig5). 45Ca2+level and the swelling of protoplasis were sharply declined when EGTA, verapamil or LaCcl3 was added into the medium(Table 1,2and3). These results indiated that Ca2+ may play an important role in 6-BA-induced swelling.

Protoplasts isolated from red-light-grown maize (Zea mays L.) coleoptiles shrank transiently upon brief exposure (e.g. 30 s) to blue light under background irradiation with red light. The maximal volume reduction (about 4% at a saturating fluence) occurred about 5 min after blue-light stimulation. The response was prevented by the anion-channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid. Red light and far-red light did not induce any comparable response. Protoplasts of different sizes and those isolated from different coleoptile positions showed similar responses. After treatment with a saturating blue-light pulse, the protoplasts became responsive to a second pulse and gained full responsiveness within 5 min, suggesting that the photoreceptor system involves a dark-reversible component. The response to continuous blue light was also found to be transient. The protoplast volume was reduced during about 6 to 9 min of irradiation and returned within the next 30 min to the control level. The response to continuous blue light was saturated at 30 pmol m-2s-1. However, when the fluence rate was enhanced 10-fold after a period of irradiation at 30 pmol m-2s-1, the protoplasts showed another shrinking response. These and other kinetic results indicate that the photoreceptor system undergoes a photosensory adaptation. Crowth in different zones of the coleoptile was inhibited by blue light transiently after pulse stimulation, as well as during continuous stimulation. It was concluded that the observed protoplast shrinking is related to the blue-light-induced inhibition of coleoptile growth.