ICAR AIEEA PG 2024 - Plant Biotechnology

Plant tissues are organized into three primary tissue systems: dermal, ground, and vascular. The vascular tissue system comprises complex conducting tissues, namely xylem (which transports water, dissolved minerals, and provides mechanical support via tracheids, vessels, xylem fibers, and xylem parenchyma) and phloem (which translocates photoassimilates). Collenchyma and parenchyma belong to the ground tissue system, while the epidermis forms the dermal tissue system.

In plant biology, light—specifically daylength (photoperiod) and associated light signals—acts as the primary environmental cue that synchronizes flowering time with seasonal progression. Plants sense the duration and quality of light via photoreceptors (phytochromes and cryptochromes), which regulate the CONSTANS (CO) transcription factor and drive the expression of the mobile flowering hormone Florigen (encoded by the FLOWERING LOCUS T / FT gene).

Exudation of sap (bleeding) from a decapitated stem of a well-hydrated plant is driven by positive hydrostatic pressure developed in the root xylem, known as Root Pressure. Roots actively absorb mineral nutrients from soil solution and accumulate them into the xylem conduits. This decreases xylem solute potential, driving osmotic influx of water from the surrounding cortex and generating positive pressure (often up to 0.1–0.2 MPa), which pushes xylem sap upward and causes guttation from hydathodes or bleeding from cuts.