SEED TREATMENT WITH PHYTOHORMONES AND CROP PRODUCTIVITY. III. PHYSIOLOGICAL/BIOCHEMICAL CHANGES IN GERMINATING SEEDS AND ROOTING CHARACTERISTICS OF WHEAT (TRITICUM AESTIVUM L.) FOLLOWING EXPOSURE TO 2,4-D

The 2,4-dichlorophenoxy acetic acid (2,4-D) is a commonly used herbicide. Over the past few years, its auxin-like action has been extensively exploited for modifying plant roots to achieve enhanced bacterial colonization and N2 fixation. We adopted seed soaking as a mode of administering 2,4-D and observed changes in seed germination and rooting characteristics of wheat (Triticum aestivum L.). Soaking of seeds in an aqueous solution containing 2,4-D (0 – 200 μg mL-1) resulted in delayed or arrested seed germination. However, the number of primary roots increased dramatically and this effect was more pronounced at higher concentrations of 2,4-D. Delay in seed germination was due to decreased metabolism of seed reserves as observed by much lowered respiration rates (loss of CO2). FTIR spectroscopy revealed a relatively slow starch degradation in 2,4-D treated seeds as observed by the intensities of the characteristic absorption peaks of a broad OH band and the fingerprint region of starch. Number of primary roots increased significantly due to soaking of seed in 2,4-D solution but showed stunted growth. Scanning electron microscopy (SEM) of roots exposed to 2,4-D in the growth medium showed a strengthening of stellar system but damaged cells at the surface. Leakage of cellular material from damaged cells caused an increased colonization of roots by bacteria (revealed by SEM) and their subsequent proliferation in the rooting medium