96 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”air. Plants respond to high temperature by inducing heat-shock proteins,
which help to maintain protein conformation, and to low temperature
by cold-shock proteins, which protect the RNA machinery. In times
of drought, plants tend to increase water absorption from the roots, to
increase its entry into the cells, and to minimize water loss from the
leaves by closure of the stomata (tiny openings on the underside of the
leaves). Oxidative stress due to ozone and ultraviolet radiation is coun-
tered by antioxidants, which are abundant in plants. Nutrient deficiency
elicits variable biochemical changes aiming at stabilizing the concen-
tration of the particular mineral in question. The stress caused by high
soil salinity is responded to by increased intracellular solute particles,
including osmotin, a small protein whose intracellular level can reach as
high as 12% of the total cell protein.
The interaction of plants and humans is subtle and sophisticated.
Over the course of history, mankind has cultivated a number of crops
and fruits selected for their taste and/or nutrition value. What usually
evades our attention is that the benefit goes both ways. These plants
achieve their “goal” of perpetuation by enticing us with their attractive
features.
5.2 Extravagant Metabolism as a Strategy for Survival
Both plants and animals need to maintain a relatively constant inter-
nal environment (homeostasis) for survival. However, unlike animals
that move around to select an optimal location, plants are stuck in one
place once their seeds are planted. To cope with fluctuations in external
conditions, plants have evolved highly diverse secondary sets of met-
abolic pathways, many of which are needed only in special situations
and not for life maintenance in normal conditions. Hence, overall plant
metabolism is many times more complicated than what we can see in an
animal. The secondary (non-essential) metabolic pathways in plants arise
through permissive genetic mutation, resulting in tremendous chemo-
diversity and increased adaptability for survival.^1 For example, phenolic