LIFE SCIENCE FOR GENERAL UNDERSTANDING: PLANTS --II

 LIFE SCIENCE FOR GENERAL UNDERSTANDING:      PLANTS --II

[ON REQUEST FROM Cdr. V. KRISHNAN]

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It would be quite astonishing, if we recognize how many different external situations are clearly perceived by plants. These include recognizing ‘light’, gravity, physical obstruction to spreading etc. Most of it may occur by perceiving a stimulus like ‘contact’, temperature, occurrence of ground water in the soil matrix and so on. Any of these can induce plant response and it may be positive [towards the stimulus] or negative [away from the stimulus].

GRAVITY, ROOT, STEM

Gravity is an environmental factor. Both stem and root perceive gravity, but respond differently for the same signal. Perception of gravity is named ‘gravi sensing’ to suggest sensing the gravity. Stem moves away from gravity while root moves towards the direction of gravity. This response is typical of these plant-parts. It is the terminal segment which ‘perceives’ the stimulus based on certain ‘grain-like’ particles in the root tip , which exert pressure signifying the factor of gravity. Root responds accordingly.

BRANCHING PATTERNS

Plant branches prefer to grow away from interference –human or any other. We can notice that new saplings start making branches only after attaining some height so that the branches away from the easy reach of persons /cattle. To start with branches may arise at lower levels; but once the interference pattern is ‘perceived’ branching is postponed until some height is reached. Note the tree branches in school / college campus where trees are close to the building. In them branches arise and spread away from the corridor so that human interference by plucking branches or leaves is avoided. Sensing signals / danger is essential for survival of plants.

OTHER SURVIVAL STRATEGIES

There are any number of tiny plants which grow to a total of 2 feet or below. These are ‘herbs’ which grow, mature and complete the life within a defined period before the arrival of extreme climate like frost or high summer. Their life ‘tenure’ is designed to begin in rain fed soil,  grow, form flowers, fruits, seeds and die before ‘climate extreme’. Only their seeds survive through bad climate; but revive upon better climate from those seeds.

Some plants merely pass the ‘bad climate’ as tiny buds ; these buds later open up and form new structures. This way also, plants manage to exist through ‘unfavourable’ conditions. Very rarely plants get eliminated outright.

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Prof. K. RAMAN