(a) Alkaloids and their significance 10 (b) Role of growth substances in agri-horticulture 10 (c) Plant indicators 10 (d)…

(a) Alkaloids Alkaloids are nitrogen-containing, basic, mostly heterocyclic secondary metabolites, usually derived from amino acids (and not from the shikimate–terpenoid pathway alone), found chiefly in angiosperms such as Papaveraceae, Solanaceae and Rubiaceae. They are bitter, often crystalline and precipitated by Mayer’s and Dragendorff’s reagents. They defend plants against herbivores. Examples: morphine and codeine from opium poppy (Papaver somniferum), quinine from Cinchona, atropine from Atropa belladonna, caffeine, nicotine, reserpine from Rauvolfia serpentina. Uses: analgesics, antimalarials, antihypertensives, muscle relaxants and anticancer drugs (vincristine and vinblastine from Catharanthus roseus). They are a basis of pharmaceutical industry, though many are toxic or addictive.

(b) Growth substances in agri-horticulture Plant growth substances are organic compounds that, at low concentration, regulate growth. Auxins (NAA, IBA) promote rooting of cuttings, prevent fruit drop and induce parthenocarpy in tomato; 2,4-D is a weedicide. Gibberellins (GA3) elongate sugarcane internodes and enlarge seedless grapes. Cytokinins (BAP, kinetin) aid tissue culture and delay senescence in leafy vegetables. Ethylene (ethephon) ripens banana, tomato and mango and induces flowering in pineapple. Abscisic acid and retardants such as CCC reduce lodging and promote dormancy. Proper dose and timing are critical: excess is harmful.

(c) Plant indicators Plant indicators are species whose presence, absence or condition reveals environmental status. Lichens (Usnea, Parmelia) vanish in SO2-polluted air and indicate air quality. Rhododendron and Calluna indicate acidic soils; Salicornia and Suaeda indicate saline soils; Eichhornia (water hyacinth) marks nutrient-rich, eutrophic water; tobacco Bel-W3 variety is sensitive to ozone; Petunia to ozone and PAN. Mosses accumulate heavy metals. Indicators give cheap, continuous monitoring of pollution, soil type, water quality and climate change, and help in site selection and mineral prospecting.

(d) Invasive species Invasive species are introduced non-native organisms that establish, spread and harm native biodiversity, economy or health. Traits: rapid growth, high seed output, vegetative spread, wide tolerance, allelopathy and absence of natural enemies. Indian examples: Lantana camara, water hyacinth (Eichhornia crassipes), Parthenium hysterophorus, Prosopis juliflora, Chromolaena odorata. Impacts: displacement of native flora, altered nutrient and water cycles, fisheries and navigation losses, allergies. Control: early detection, mechanical removal, biological agents (Neochetina weevils on water hyacinth, Zygogramma beetle on Parthenium), and restoration; the Convention on Biological Diversity (Aichi/Kunming–Montreal) calls for management of invasive alien species.

(e) IUCN Red List categories The IUCN Red List of Threatened Species, run by IUCN’s Species Survival Commission, assesses extinction risk using quantitative criteria A–E (population decline, small range, small or declining population, extinction probability). Categories: Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), Data Deficient (DD) and Not Evaluated (NE); CR, EN and VU together are “threatened”. Examples: Chinese pangolin (CR), Indian pangolin (EN), Great Indian Bustard (CR). The List guides conservation priorities and is distinct from CITES, which regulates trade.