Kaur Prabhdeep, Gupta Anil K, Kaur Narinder
Department of Biochemistry and Chemistry, Punjab Agricultural University, Ludhiana 141 004, India.
Indian J Biochem Biophys. 2005 Jun;42(3):161-5.
When embryonated and de-embryonated cotyledons of cowpea (Vigna unguiculata L.) were kept for germination, only embryonated cotyledons (EC) developed into seedlings. alpha-Amylase activity appeared late in de-embryonated cotyledons (DEC), but increased and matched with that of EC on 4th day, and thereafter started declining. A higher content of reducing sugars may be one of the factors in down regulating the activity in DEC after 4th day, in comparison to EC, where it continued increasing. Addition of GA3 to DEC did not increase the activity significantly, suggesting that GA3 was not a limiting factor for amylase initiation. Addition of 1 mM chlorocholine chloride (CCC) to DEC decreased activity by about 50%, suggesting that GA3 might partly be synthesized in the DEC and hence the activity could be initiated independent of embryo. However, for mobilization of starch, amylase activity has to be sustained for a longer period, for which sink strength in the form of shoot and root is essential. Unlike cereals, where embryo is required for induction of amylase, the process of amylase induction in germinating cowpea seeds appear to be different. Purification of alpha-amylase from EC and DEC by DEAE-cellulose and Sephadex G-150 column chromatography revealed three peaks in EC, and only one in DEC, indicating that gibberellin present in DEC could induce only one form of amylase. Amylase from DEC had higher K(m) value (0.33 mg ml(-1) of starch), as compared to the corresponding K(m) value in EC (0.11 to 0.16).
将豇豆（Vigna unguiculata L.）的带胚和去胚子叶进行催芽时，只有带胚子叶（EC）能发育成幼苗。去胚子叶（DEC）中的α-淀粉酶活性出现较晚，但在第4天增加并与带胚子叶的活性相当，此后开始下降。与带胚子叶中还原糖含量持续增加相比，较高的还原糖含量可能是第4天后去胚子叶中酶活性下调的因素之一。向去胚子叶中添加赤霉素（GA3）并没有显著增加其活性，这表明GA3不是淀粉酶起始的限制因素。向去胚子叶中添加1 mM氯化胆碱（CCC）可使活性降低约50%，这表明GA3可能部分是在去胚子叶中合成的，因此其活性可以独立于胚启动。然而，为了淀粉的动员，淀粉酶活性必须持续较长时间，而这需要地上部和根部形式的库强。与谷物不同，谷物诱导淀粉酶需要胚，而豇豆种子萌发过程中淀粉酶的诱导过程似乎有所不同。通过DEAE-纤维素和Sephadex G-150柱色谱法从带胚子叶和去胚子叶中纯化α-淀粉酶，结果显示带胚子叶中有三个峰，而去胚子叶中只有一个峰，这表明去胚子叶中存在的赤霉素只能诱导一种形式的淀粉酶。与带胚子叶中相应的米氏常数（K(m)）值（0.11至0.16）相比，去胚子叶中的淀粉酶具有更高的K(m)值（0.33 mg ml(-1)淀粉）。
