Aging leaves: sex and death.

Aging leaves: Sex and death

Withering leaves mark the end of a perennial plant's photosynthesis for that growing season. This leafy demise has at least one fortifying benefit: It enables plants to recover nutrients from the leaves and divert them to needy parts elsewhere. Researchers are now trying to determine the conditions under which plants sometimes take the opposite approach, prolonging photosynthesis by delaying leaf death.

For two years, Ying Lu and Maxine A. Watson of Indiana University in Bloomington studied leaf survival in several colonies of mayapple, a fruit-bearing perennial. They found that leaves survived eight to 14 days longer in plants that reproduced sexually and bore fruit and in plants with larger-than-normal new rhizomes, or underground stems. This suggests the plants replenish the extra energy expended in sexual reproduction by extending the photosynthetic period, says Lu. Carbohydrates produced in photosynthesis apparently provide more sustenance than does the release of mineral nutrients stored in dying leaves, she concludes. The researchers observed that mayapples undergoing asexual reproduction seem to favor earlier leaf death and nutrient release. Other scientists have found similar patterns of leaf survival in different plants.