(a) Describe different types of endosperm development in angiosperms. What is the significance of aleurone tissue? Mention the…

(a) Types of endosperm development; aleurone; function of endosperm

The endosperm develops from the primary endosperm nucleus, formed by triple fusion of a male gamete with the two polar nuclei. It is therefore usually triploid (3n). There are exceptions: it is 2n in Oenothera, whose embryo sac has four nuclei; 5n in *Fritillaria*-type embryo sacs; and 15n in Peperomia. There are three types of development.

Nuclear type (the commonest):

• The primary endosperm nucleus divides repeatedly without wall formation, producing many free nuclei arranged at the periphery around a large central vacuole.
• Walls then form from the periphery towards the centre (centripetally), and the endosperm becomes wholly or partly cellular.
• Examples: maize, wheat, rice, Capsella and sunflower. In coconut, the outer part becomes cellular (the white "meat"), while the centre stays free-nuclear as liquid endosperm ("coconut water").
• Cellular type: every nuclear division, including the first, is followed by wall formation, so the endosperm is cellular from the start. Endosperm haustoria often form at the micropylar or chalazal end. Examples: Datura, Petunia, Impatiens, Adoxa and many Lamiaceae and Scrophulariaceae.

Helobial type (intermediate, typical of the order Helobiales/Alismatales): the first division is followed by a transverse wall, which gives a large micropylar chamber and a small chalazal chamber.

• The micropylar chamber develops in the nuclear way, with free nuclei first and walls later.
• The chalazal chamber stays small, with few nuclei, and often degenerates or acts as a haustorium.
• Examples: Eremurus, Sagittaria, Asphodelus.

Aleurone tissue: significance

• Structure: the outermost one to three layers of cereal endosperm (one layer in wheat, maize and rice, about three in barley). Its cells are living and rich in protein bodies (aleurone grains), phytin, lipids, minerals and B vitamins. The inner starchy endosperm is dead at maturity.
• Role in germination: during germination the embryo releases gibberellin. The aleurone responds by making and secreting α-amylase, proteases and other hydrolases into the starchy endosperm, which digest starch and protein into sugars and amino acids for the growing seedling. This is the basis of malting in brewing.
• Nutrition: aleurone contributes much of the protein, minerals, vitamins and dietary fibre of bran. It is lost in highly polished rice and white flour.
• Genetics: anthocyanin in the aleurone gives coloured maize kernels and was used by McClintock to study transposons. It is also the tissue in which "xenia" (the effect of pollen on the endosperm) is seen.

Function of endosperm in the seed

• It nourishes the developing embryo, whose growth depends on it.
• In albuminous seeds (cereals, castor, coconut) it stores starch, proteins or oils for the seedling. In exalbuminous seeds (pea, bean, groundnut) it is absorbed by the embryo and the food is stored in the cotyledons.
• It regulates seed size and embryo development, and it is the main source of human food: cereals provide most of the world's calories.

(b) Brassicaceae (Cruciferae): features and economic species

Characteristic features

• Habit: mostly annual or perennial herbs with a pungent watery sap. Myrosin cells release mustard oils (isothiocyanates) from glucosinolates when the tissue is damaged. Roots are sometimes swollen, as in radish and turnip.
• Leaves: alternate, simple, often lyrate or pinnatifid, exstipulate, and frequently in a basal rosette.
• Inflorescence: a raceme, usually corymbose when young, without bracts (ebracteate).

Flower: bisexual, actinomorphic, hypogynous and tetramerous.

• Calyx: four sepals in two whorls (2 + 2), the inner lateral pair often pouched (saccate) at the base.
• Corolla: four free petals with long claws, arranged diagonally in the form of a cross (cruciform).
• Androecium: six stamens, two short outer (lateral) and four long inner (median) ones, a condition called tetradynamous. Green nectaries lie at the base of the short stamens.
• Gynoecium: bicarpellary and syncarpous, with a superior ovary, one locule divided into two by a false septum (the replum and its membrane), and parietal placentation.
• Fruit: a siliqua, long and dehiscing from below upwards by two valves leaving the replum with its seeds, as in mustard and radish. Some have a silicula (short and broad, as in Capsella and Iberis), or indehiscent and jointed fruits (radish, Crambe).
• Seeds: without endosperm, with a curved embryo and oily cotyledons.
• Floral formula: Ebr ⊕ ⚥ K2+2 C4 A2+4 G(2).

Five economic species

• Brassica juncea (Indian mustard, rai): the main oilseed of Rajasthan, Haryana and Uttar Pradesh. It supplies mustard oil, cake and condiment seed. Pusa Bold is a well-known variety. The transgenic hybrid DMH-11 was approved for environmental release in 2022, a decision that remains under legal and public debate.
• Brassica rapa (toria, yellow and brown sarson, turnip): an oilseed and a vegetable.
• Brassica napus (gobhi sarson, rapeseed; "canola" types are low in erucic acid and glucosinolates): edible oil and meal.
• Brassica oleracea (cole crops): cabbage (var. capitata), cauliflower (var. botrytis), broccoli (var. italica), knol-khol (var. gongylodes) and Brussels sprouts (var. gemmifera). They are rich in vitamin C and anticancer glucosinolates.
• Raphanus sativus (radish): the root is eaten as a vegetable and the pods (mungra) are also eaten.

Other examples:

• Eruca sativa (taramira): oilseed of arid areas.
• Lepidium sativum (garden cress, halim): iron-rich seeds.
• Iberis (candytuft): ornamental.
• Isatis tinctoria (woad): blue dye.
• Arabidopsis thaliana: the model plant of genetics.

(c) Millets: nutritional superiority, botanical names, advantages

Nutritional superiority (per 100 g, approximate values from Indian food composition tables):

• Minerals: finger millet (ragi) has about 350 mg of calcium, roughly nine times whole wheat and around forty times polished rice. Pearl millet (bajra) has about 6 mg of iron, against under 1 mg in polished rice.
• Fibre: most millets are whole grains with 7–12% dietary fibre, far more than polished rice. They have a low to moderate glycaemic index, which helps in diabetes management.
• Protein: similar to wheat (10–12% in foxtail, proso and bajra) but lower in ragi (about 7%). Their proteins are better balanced in some amino acids, such as methionine in ragi. Millets are gluten-free, suiting coeliac patients.
• Other nutrients: they are rich in B vitamins, magnesium, phosphorus and antioxidants (polyphenols). Bajra also contains useful fats.
• A caution: anti-nutrients such as phytates and tannins, and goitrogens in pearl millet, are reduced by soaking, germinating (malted ragi) and fermenting.

Millets grown in India

• Cenchrus americanus (syn. Pennisetum glaucum): pearl millet or bajra.
• Sorghum bicolor: jowar.
• Eleusine coracana: finger millet or ragi.
• Setaria italica: foxtail millet or kangni.
• Panicum miliaceum: proso millet or cheena.
• Panicum sumatrense: little millet or kutki.
• Echinochloa frumentacea: barnyard millet or sanwa.
• Paspalum scrobiculatum: kodo millet.

Advantages of cultivating millets

• Water: most are C4 plants that are hardy on marginal, rainfed land. They need about 350–500 mm of water, compared with over 1,200 mm for rice.
• Duration: short (60–100 days), which fits intercropping and contingency planting.
• Inputs: they need few fertilisers and pesticides and have fewer pest problems, and many store well for years.
• Climate resilience: they tolerate heat, drought and salinity, which makes them "climate-smart" crops. They also have a smaller carbon and water footprint.
• Food and livelihood security: they support tribal and dryland farmers, provide fodder from the stover, and fight "hidden hunger".
• Policy support: the UN International Year of Millets (2023) was proposed by India. Millets are promoted as "Shree Anna", included in the public distribution system and midday meals, supported through state millet missions such as Odisha's (2017), and the Indian Institute of Millets Research in Hyderabad has been made a global centre of excellence.