Have you ever seen a rice flower? Did you know that rice plants look out for a certain daytime-length to flower? Wondered how rice gets its color – or thought that there may be a difference between “brown rice” and “red rice” beyond color? Ever imagined that sowing depth of paddy seed matters to whether the rice you eat is organic? Have you heard of a rice embryo breathing?
Read on to find out why rice anatomy matters to the creation and preservation of all the hundreds of beautiful rice varieties India boasts of!
Cultivated rice | The rice plant | The importance of “bran” & its Colours | Sources & Further Reading
The cover image for this article, also shown to the left above, was very generously provided by Rashmimala: Paddy-Waya (From a series, Speaking of Places) Casein tempera on archival paper 31 cm x 24 cm 2017-18. Right: Zenker, J.C., Merkantilische Waarenkunde (1831-1835)
cultivated rice
Rice is a grass, the only major crop in the tribe Oryzeae. Carl von Linneaus described the genus Oryza with a single species Oryza sativa in his Species Plantarum in 1753; there have been debates since about the origins and constitution of this species, but the recent view (as of 1965) is represented in the diagram below:
We do not know precisely when rice cultivation began, but we do know rice was being cultivated at least 10,000 years ago and that it was domesticated from its wild ancestor O. rufipogon. There are now two major subgroups of rice, indica and japonica. Again, this has led experts to conclude that there must have been two centers of origin: one in the tropical regions of South Asia where indica rice varieties dominated and the other near Central China where japonica rice dominated.
The debate on origins remains unsettled largely because of the nature of rice itself: domesticated rice and its wild ancestors still cross naturally in farmers’ fields, and “weedy” rice is an irritant for farmers trying to cultivate specific selections with desired qualities. But these problems point to the extraordinary diversity in rice germplasm. Rice has evolved and adapted in and to an astonishingly diverse array of environments from the hot deserts of Iran and Egypt to deeply flooded river deltas [the Mekong in Vietnam, the Chao Phraya in Thailand, the Irrawady in Myanmar, and the Ganges–Brahmaputra in Bangladesh and eastern India], from hilly, mountainous and rocky landscapes, to areas with saline, alkali, or acid sulfate soils. India forms a major part of the region of early cultivation and is traditionally rich in the genetic diversity including the wild progenitors (Patra et al., 2016: 2).
| INDICA | JAPONICA |
| long, wide to narrow, light green leaves | thin, light green leaves |
| profuse tillering (many stalks from one plant) | medium tillering |
| mostly taller plants | short to intermediate size |
| usually long and thin grains | usually short and round grains |
This background is important for understanding the ingenuity and skill of early farmers, who selected, developed, and preserved the purity of thousands of native or folk rice varieties. They often named rices based on certain key anatomical features or morphological traits. Rice plant anatomy is critical to conserving folk rices, with all their nutraceutical and culinary properties intact.
the rice plant
The rice plant consists of the following, from the ground up:
1. A shallow ROOT SYSTEM. 95% of the roots are found in the top 0 to 0.2 m of soil. Some introduced HYVs compelled farmers to buy tractors instead of using traditional ploughs, because of differences in sowing depths required for optimal growth. This is one of many ways in which the green revolution commercialized farming and created debt traps in agrarian communities. Switching to tractors meant also the further loss of pastoral lifestyles—fewer cows and bulls meant less dung and manure for the fields. In combination with increased fertilizer use, this took a toll on soil health.
2. The CULM, or jointed stem of the rice, is made up of a series of nodes and internodes. Each node has one leaf and one bud that can develop into a TILLER. The nodes of the main stem can produce secondary tillers, and those can produce tertiary tillers. How many tillers a plant produces depends on the variety, but also on growing conditions and crop management.
Shorter lower internodes mean that the plant will be more resistant to lodging or falling over when the panicles ripen and add weight to the top of the plant. The thickness and height of stems also affects susceptibility (or resistance) to lodging. A lodged rice plant produces poor quality grains.
3. LEAVES grow alternately on the stem, one leaf per node. The last leaf wrapping the panicle is called the panicle leaf or flag leaf. Leaf architecture and behavior are key ways in which to tell different rice cultivars apart.
4. RICE FLOWERS: Panicles are the top part of the rice plant, which form the rice inflorescence, carried on the last inter-node. Single panicles can bear between 150 and 350 spikelets, which are a structural unit of the inflorescence that each contain one grain at maturity.
Rice is self-fertile or self-pollinating (autogamous), so each flower has male (the anthers containing pollen) and female (the ovary) reproductive parts. [This is unlike allogamous plants like maize where fertilization is by the pollen from another flower of the same or different plant.]
Native rice varieties are photosensitive, which is to say that they sense daylight hours during the flowering period. A photoperiod longer or shorter than the “optimum” for each variety has been shown to delay flowering, the delay depending upon the cultivar’s degree of sensitivity. Some long-duration traditional rice varieties are sowed with the July-August/SouthWest monsoon rains and they have adapted to develop in tandem with the November-December/NorthEast monsoon. HYVs and other institutionally bred varieties are intentionally not-photosensitive and short duration, and were failures during the Samba/Kharif cropping season.
Rice flowers bloom only at a specific time of day, and then only for several minutes. They are elusive little blossoms on whose whims the world depends for its food! Below is a panicle whose flowers just finished blooming–and the fallen petals are strewn on the water in the paddy fields below.
5. GRAIN or paddy has three main parts:
- The hull or husk, which becomes chaff while milling (20% of the grain)
- Caryopsis or “brown rice” kernel (70% kernel, 9% bran) and the
- Germ nested within, in the ventral part of the spikelet (1%)
RICE HULL is high in silica, and poses threat to milling equipment as also to environment—its sheer bulk silica content make it resistant to easy degradation.
The BROWN RICE KERNEL consists or a bran layer (testa and aleurone layers), a germ and the starchy center of the grain, intended to feed the rice embryo.
- The thin fibrous layer immediately below the hull is the pericarp. Usually, it is the pericarp (not the hull) that gives a rice grain its color. If it is reddish, then the grain gets called “red rice”! The pericarp is protective against moulds and quality deterioration.
- Beneath this is testa or tegmen layer, just a few cells in thickness, rich in oil and protein.
- Immediately under the testa or tegmen layer is the aleurone layer—sometimes also called the “BRAN LAYER” because of its high percentages of oil, protein, vitamins and minerals. Because of its high oil content, the bran is easily affected by oxidation. If brown rices turn rancid faster than polished ones, the reasons are in the testa and in this aleurone layer.
So now you know–rice of any pericarp color, hulled but bran layers intact is a “brown rice”. The term refers to the complete, edible grain–not really to its color at all.
The importance of “bran” & its COLours
The pericarp, testa, and aleurone layers are commonly referred to as “rice bran,” to which “most of the important nutritional compounds are bound.” The bran layer is thus “the main site of micro-and macro-nutrients and a range of important phytochemicals, such as oryzanols, tocopherols, phenolic compounds, flavonoids, and anthocyanin that impart an overall nutritional property of rice …” (Ray et al. 2021: 153)
Differently colored bran means different nutritional content: “About 38% to 60% of the total polyphenol content is present in grains of light brown rice. In contrast, the red and black pericarp of coloured grains contains around 81% of the polyohenols. The natural hues of rice bran colour have a profound effect in determining the nutritional content of grains” (Ray et al. 2021: 153).
This bran layer is generally reduced or removed entirely in milling. The higher the milling degree, the greater percentage of bran is removed. Fully milled or “polished” rice may also have the germ removed, and the grain is thus reduced to just starch.
Most traditional cuisines in India recognized the value of these bran layers—and manual milling could never polish rice the ways power-driven milling can, leading us to surmise that “white rice” never really existed prior to powered machine milling systems in the early part of the 20th century.
Bearing testimony to earlier understandings of bran value: Garib sal (the “poor rice” from West Bengal) is somewhat ironically a variety with ∼15 mg/kg silver concentrated in the aleuronic layer of the rice bran, or in proportion to the silver present in the soil—local communities consume the unpolished rice as a treatment for gastroenteric ailments, and the polished rice at other times [Sengupta et al. 2017]. Other grains like njavara or varieties with known medicinal properties are never polished. Still others like kullan thondi may be only semi-polished after parboiling for reasons both of nutrition and taste. [Parboiling allows the movement of nutrients from the bran layer to the inner part of the grain thus making the vitamins available even in fully milled rice.]
The EMBRYO is the living organism in the grain, which respires by taking in oxygen in the air, and consumes the starch in the endosperm while simultaneously releasing moisture and heat. This explains why grains during storage have the tendency to decrease in weight as a result of the loss in moisture and dry matter content in the endosperm. The embryo is removed during milling resulting in an indented shape at one end of the grain and stabilising weight.
Only when the husk, the pericarp, the bran and the embryo are all removed, only the STARCHY ENDOSPERM remains. Because of its high percentage of carbohydrates, its energy value is high. It may have trace amounts of aromatic volatiles from the bran, but these will dissipate as the rice becomes older. Traditional communities would only mill aromatic rice in small quantities as needed to preserve taste, thereby allowing the paddy to age while retaining and even improving its texture and flavor.
SOURCES CONSULTED
- “The Rice Plant” on Rice Hub
- Belsnio, B. 1992. “Physical grain characteristics of paddy/milled rice and its grades and standards.” In: Towards integrated commodity and pest management in grain storage: A Training Manual for application in humid tropical storage systems. Edited by R.L. Semple, P.A. Hicks, J.V. Lozare, and A. Castermans. Proceedings and selected papers from the Regional Training Course on Integrated Pest Management Strategies in Grain Storage Systems, conducted by the National Post Harvest Institute for Research and Extension (NAPHIRE), Department of Agriculture, June 6-18, 1988, Philippines.
- Patra, Bhaskar C., Soham Ray, Umakanta Ngangkham, Trilochan Mohapatra. 2016. “Rice” In: Genetic and Genomic Resources for Grain Cereals Improvement. Eds Mohar Singh and Hari D. Upadhyaya. London: Academic Press.
- Ray, Sandipan, Debal Deb, and Mousumi Poddar Sarkar. “Colour based nutraceutical potential of some traditional rice (Oryza sativa L. ssp. indica) varieties of India.” Indian Journal of Natural Products and Resources (IJNPR)[Formerly Natural Product Radiance (NPR)] 12.1 (2021): 153-157.
- Sen Gupta, Soujit, Ananya Baksi, Priyabrata Roy, Debal Deb, and Thalappil Pradeep. “Unusual Accumulation of Silver in the Aleurone Layer of an Indian Rice (Oryza sativa) Landrace and Sustainable Extraction of the Metal.” ACS Sustainable Chemistry & Engineering 2017: 5(9), 8310-8315 DOI: 10.1021/acssuschemeng.7b02058
- Kennedy, G., B. Burlingame and Nguu Nguyen. 2002. “Nutrient impact assessment of rice in major rice-consuming countries.” International Rice Commission Newsletter Vol. 51. United Nations: FAO
- Vergara, B.S. and T.T. Chang. 1985. The Flowering Response of the Rice Plant to Photoperiod. Manila: IRRI
