Neuenschwander U, Suter M, Brunold C
Pflanzenphysiologisches Institut der Universität Bern, Altenbergrain 21, Bern, Switzerland.
Plant Physiol. 1991 Sep;97(1):253-8. doi: 10.1104/pp.97.1.253.
The effect of 0.5 millimolar O-acetyl-l-serine added to the nutrient solution on sulfate assimilation of Lemna minor L., cultivated in the light or in the dark, or transferred from light to the dark, was examined. During 24 hours after transfer from light to the dark the extractable activity of adenosine 5'-phosphosulfate sulfotransferase, a key enzyme of sulfate assimilation, decreased to 10% of the light control. Nitrate reductase (EC 1.7.7.1.) activity, measured for comparison, decreased to 40%. Adenosine 5'-triphosphate (ATP) sulfurylase (EC 2.7.7.4.) and O-acetyl-l-serine sulfhydrylase (EC 4.2.99.8.) activities were not affected by the transfer. When O-acetyl-l-serine was added to the nutrient solution at the time of transfer to the dark, adenosine 5'-phosphosulfate sulfotransferase activity was still at 50% of the light control after 24 hours, ATP sulfurylase and O-acetyl-l-serine sulfhydrylase activity were again not affected, and nitrate reductase activity decreased as before. Addition of O-acetyl-l-serine at the time of the transfer caused a 100% increase in acid-soluble SH compounds after 24 hours in the dark. In continuous light the corresponding increase was 200%. During 24 hours after transfer to the dark the assimilation of (35)SO(4) (2-) into organic compounds decreased by 80% without O-acetyl-l-serine but was comparable to light controls in its presence. The addition of O-acetyl-l-serine to Lemna minor precultivated in the dark for 24 hours induced an increase in adenosine 5'-phosphosulfate sulfotransferase activity so that a constant level of 50% of the light control was reached after an additional 9 hours. Cycloheximide as well as 6-methyl-purine inhibited this effect. In the same type of experiment O-acetyl-l-serine induced a 100-fold increase in the incorporation of label from (35)SO(4) (2-) into cysteine after additional 24 hours in the dark. Taken together, these results show that exogenous O-acetyl-l-serine has a regulatory effect on assimilatory sulfate reduction of L. minor in light and darkness. They are in agreement with the idea that this compound is a limiting factor for sulfate assimilation and seem to be in contrast to the proposed strict light control of sulfate assimilation.
研究了向营养液中添加0.5毫摩尔O - 乙酰 - L - 丝氨酸对在光照或黑暗条件下培养的，或从光照转移至黑暗条件下的浮萍（Lemna minor L.）硫酸盐同化作用的影响。从光照转移至黑暗后的24小时内，硫酸盐同化作用的关键酶——腺苷5'-磷酸硫酸转移酶的可提取活性降至光照对照的10%。作为对比测定的硝酸还原酶（EC 1.7.7.1.）活性降至40%。腺苷5'-三磷酸（ATP）硫酸化酶（EC 2.7.7.4.）和O - 乙酰 - L - 丝氨酸巯基化酶（EC 4.2.99.8.）的活性不受转移的影响。当在转移至黑暗时向营养液中添加O - 乙酰 - L - 丝氨酸，24小时后腺苷5'-磷酸硫酸转移酶活性仍为光照对照的50%，ATP硫酸化酶和O - 乙酰 - L - 丝氨酸巯基化酶活性再次不受影响，而硝酸还原酶活性如之前一样下降。转移时添加O - 乙酰 - L - 丝氨酸导致在黑暗中24小时后酸溶性SH化合物增加100%。在持续光照下相应的增加为200%。转移至黑暗后的24小时内，在没有O - 乙酰 - L - 丝氨酸的情况下，(35)SO(4) (2-)向有机化合物中的同化作用下降了80%，但在其存在时与光照对照相当。向在黑暗中预培养24小时的浮萍添加O - 乙酰 - L - 丝氨酸会诱导腺苷5'-磷酸硫酸转移酶活性增加，以至于在额外9小时后达到光照对照恒定水平的50%。放线菌酮以及6 - 甲基嘌呤抑制了这种效应。在同一类型的实验中，在黑暗中额外24小时后，O - 乙酰 - L - 丝氨酸诱导从(35)SO(4) (2-)掺入半胱氨酸的标记增加了100倍。综上所述，这些结果表明外源性O - 乙酰 - L - 丝氨酸对浮萍在光照和黑暗条件下的同化性硫酸盐还原具有调节作用。它们与该化合物是硫酸盐同化的限制因素这一观点一致，并且似乎与所提出的严格光照控制硫酸盐同化的观点相反。
