Cysteine proteinases and programmed cell death in tomato

特定细胞和组织的受控自杀或程序性死亡是大多数多细胞生物发育的自然组成部分。在植物中，导水组织（树木中的“木材”）的形成完全依赖于直接参与水传导的细胞的程序性死亡。这一过程在支持组织、树木保护性树皮的形成以及植物对病原体入侵的反应中也很重要。衰老，导致秋天落叶的过程也是程序性细胞死亡的结果。然而，如何在植物中控制这一过程还没有完全了解。我们正在研究一组特定的酶在不同植物中程序化细胞单独发生中的作用，使用番茄作为我们的模型系统。各种蛋白质消化酶在死亡过程的早期和晚期都起着关键作用。了解细胞和植物如何控制酶何时何地出现以及它们如何被激活，应该使我们能够更全面地了解控制植物细胞死亡过程的整个程序。 我们在番茄中发现的一种酶与发芽种子中营养细胞的死亡以及允许花粉从花中释放的细胞的死亡是共同的。 这种酶在程序后期起作用。我们分离出的第二种和第三种酶似乎都在死亡程序的早期起作用，但它们都是许多细胞死亡事件的共同点。 在每种情况下，编码酶的基因只有一个拷贝，所以它们对植物来说似乎都非常重要。非常相似的酶存在于关系非常远的豌豆和蓖麻子植物中。我们继续的实验将试图确定这些酶以及相关的酶在植物的生命中有多重要。 这项研究的未来意义将是微调涉及程序化细胞的事件的时间，如果实脱落、种子灌浆期间的植物衰老、果实成熟、木材形成等，协助收获，提高作物产量，延长水果保质期，提高木材产量和质量。

The controlled suicide, or programmed death, of particular cells and tissues is a natural part of development in most multicellular organisms. In plants, the formation of the water conducting tissue, the "wood" in trees,  is absolutely dependent on the programmed death of the cells that will be directly involved in water conduction. The process is also important in the formation of supportive tissues, the protective bark of trees, and in the response of plants to pathogen invasion. Senescence, the processes leading to leaf fall in autumn is also a consequence of programmed cell death. How the process is controlled in plants, however, is not fully understood. We are investigating the role of a group of particular enzymes involved in separate occurrences of programmed cell in various plants, using tomato as our model system. The various protein digesting enzymes have key roles in  both early and late stages of the death process. Understanding of how the cells and the plant control where and when the enzymes appear and how they are activated should allow us to gain a more complete understanding of the entire program controlling the plant cell death process.     One of the enzymes that we have found in tomato is common to the death of nutritive cells in the germinating seed and to the death of cells that allows for release of pollen from the flowers.  This enzyme works late in the program. A second and a third enzyme we have isolated both seem to work earlier in the death program, but all are common to a number of cell death events.  In each case there is only one copy of the gene coding for the enzyme, so all of them seem to be extremely important to the plant. Very similar enzymes exist in very distantly related pea and castor bean plant. Our continued experiments will attempt to determine just how important these, and related enzymes, are in the life of the plant.   Future implications of the research would be to fine tune the timing of events involving programmed cell, such as fruit drop, plant senescence during seed filling, fruit ripening, wood formation, etc., to assist in harvest, improve crop yield, extend fruit shelf-life and improve wood production and quality.