(a) Describe the development of female gametophyte in angiosperms with the help of suitable illustrations. (20 marks) (b) Give…

(a) Development of the Female Gametophyte in Angiosperms

Megasporogenesis: in the young ovule, a hypodermal cell of the nucellus near the micropyle enlarges to become the megaspore mother cell (MMC, 2n), with dense cytoplasm and a prominent nucleus. It undergoes meiosis to form a linear tetrad of four haploid megaspores. Three, towards the micropyle, degenerate, and the chalazal megaspore remains functional.

Megagametogenesis: the functional megaspore enlarges and its nucleus divides mitotically. The two nuclei move to opposite poles, with a central vacuole between them (2-nucleate stage). Each divides again to give four nuclei, two at each pole (4-nucleate stage), and a third mitosis gives four nuclei at each pole (8-nucleate stage).

Cell organisation: three nuclei at the micropylar end become cells, forming the egg apparatus: one egg cell and two synergids, with a filiform apparatus that guides the pollen tube. Three nuclei at the chalazal end form the antipodal cells, which may proliferate, as in grasses. One nucleus from each pole, the polar nuclei, moves to the centre and fuses into the diploid secondary nucleus of the large central cell.

The mature embryo sac is thus 7-celled and 8-nucleate, in an ovule surrounded by integuments.

Types: in the monosporic Polygonum type one megaspore forms the sac (as in maize and most angiosperms); in the bisporic type (Allium) two megaspore nuclei contribute; in the tetrasporic type (Fritillaria, Lilium, Peperomia) all four do, and the number of nuclei and cells varies.

(b) Ethnomedicinal Plants of Fabaceae, Euphorbiaceae and Liliaceae (Liliaceae is taken in its classical sense.)

Fabaceae:

• Abrus precatorius (gunja): leaf and root, used for cough, sore throat and as an anti-inflammatory; seeds are highly poisonous (abrin).
• Glycyrrhiza glabra (mulethi): root, used for cough, ulcer and sore throat.
• Mucuna pruriens (kapikachhu): seeds, used for Parkinson's disease (they contain L-DOPA) and as a nerve tonic and aphrodisiac.

Euphorbiaceae:

• Ricinus communis (castor): seed oil, a purgative, and leaves used for rheumatic pain.
• Euphorbia hirta (dudhi): whole plant, used for asthma, dysentery and lactation.
• Acalypha indica (kuppameni): leaf, used for skin disease, wounds and as an expectorant.

Liliaceae:

• Aloe vera: leaf gel, used for burns, wounds and constipation (leaf latex).
• Asparagus racemosus (shatavari): tuberous root, used as a galactagogue and female tonic.
• Gloriosa superba (kalihari): tuber, used for gout and arthritis, as it contains colchicine; it is poisonous.

(c) Secondary Metabolites and Their Importance in Taxonomy Secondary metabolites are organic compounds that are not directly involved in growth, development or primary metabolism (unlike sugars, amino acids and lipids), are formed from primary metabolites, and are often restricted to particular taxa. They serve defence, pollinator attraction and signalling. Main classes: alkaloids, terpenoids, phenolics (flavonoids, tannins) and glycosides.

Importance in taxonomy (chemotaxonomy): their distribution is characteristic of groups and genetically controlled, so they supply additional characters. Examples: betalains in Caryophyllales, which exclude anthocyanins; glucosinolates in Brassicales; tropane alkaloids in Solanaceae; sesquiterpene lactones in Asteraceae; essential oils in Lamiaceae; benzylisoquinoline alkaloids in Papaveraceae. Betalains support separating Caryophyllales from other families, and flavonoid patterns help in resolving relationships within genera and detecting hybrids.

Analysis uses TLC, HPLC, GC-MS and NMR. Limitations: unrelated groups may evolve similar compounds convergently, so chemical data should be combined with morphology and molecular data.