Age-dependent changes of the ion content and the circadian leaf movement period in the Phaseolus pulvinus

The circadian movement of the lamina of primary leaves of Phaseolus coccine us L, depends on circadian changes of the K+, Cl- and (depending on the Cl- availability) malate content in the swelling and shrinking motor cells of the laminar pulvinus. After sowing in soil, the laminar pulvinus develops w ithin about 26 days. When the leaves emerge from the soil (about 6 days aft er sowing) and the pulvinus starts with the diurnal movement (about 9 days after sowing) the pulvinar dimensions are about half of those of the mature pulvinus. The anatomical structure, however, is basically the same as in t he developed pulvinus. In soil-grown plants, the K+, Cl- and malate content as well as the period length of the circadian leaf movement rhythm change in the developing pulvinus. In the embryo of the dry seed, the Cl- content is low (0.03 mmol g(-1) DW), the K+ content, however, 22-fold higher than t he Cl- content. When the leaves emerge from the soil, the pulvinar K+ and C l- content is the same as in the whole embryo of the dry seed. In the devel oping pulvinus the K+ content increases by a factor of 2 and the Cl- conten t by a factor of 41 in the mature pulvinus. The pulvinar malate content inc reases between the 6th and 10th day from about 40 to 180 mu mol g(-1) DW, t hen decreases until the 17th day and remains thereafter on a low level (aro und 80 mu mol g(-1) DW). These results indicate that the Cl- availability i ncreases in the developing pulvinus with age. It explains furthermore why i n young leaves malate was found as counterion to K+ in the osmotic leaf mov ement motor, in older ones, however, Cl-. The circadian leaf movement start s 9 days after sowing. The period length decreases during the development o f the pulvinus from 31.3 to 28.6 h in leaves of intact soil-grown plants. I n leaves which were cut from the plants and immersed with their petioles in distilled water, the age dependent decrease of the period length is also f ound. However, the period lengths are shorter by more than I h than in the leaves of intact plants. The increasing Cl- availability in the developing pulvinus does not seem to be the cause for the age dependent shortening of the period length, because the period length in 22 days old Cl--deprived pu lvini is the same as in 22 days old pulvini with a high Cl- content.