https://www.cell.com/trends/plant-science/pdf/S1360-1385(09)00043-0.pdf

Not just a grain of rice: the quest for quality

Background Quality is a powerful engine in rice value chain upgrading. However, there is no consensus on how “rice quality” should be defined and measured in the rice sector. Scope and approach We adopt a Lancasterian definition of rice quality as a bundle of intrinsic and extrinsic attributes. We then review how rice quality is (i) perceived and defined by consumers and industry stakeholders in rice value chains in Southeast and South Asia; (ii) measured and defined by food technologists; and (iii) predicted through genetics. Key findings and conclusions Consumers are heterogeneous with respect to their perceived differentiation of rice quality among regions, countries, cities, and urbanization levels. Premium quality is defined by nutritional benefits, softness and aroma in Southeast Asia, and by the physical appearance of the grains (uniformity, whiteness, slenderness), satiety, and aroma in South Asia. These trends are found to be consistent with industry perceptions and have important implications for regional and national breeding programs in terms of tailoring germplasm to regions and rice varieties to specific local market segments. Because rice is traded internationally, there is a need to standardize definitions of rice quality. However, food technologists have not reached unanimity on quality classes and measurement; routine indicators need to be complemented by descriptive profiles elicited through sensory evaluation panels. Finally, because rice quality is controlled by multiple interacting genes expressed through environmental conditions, predicting grain quality requires associating genetic information with grain quality phenotypes in different environments.

Rice quality: How is it defined by consumers, industry, food scientists, and geneticists?

Abiotic stresses have a detrimental impact on plant growth and productivity and are a major threat to sustainable crop production in rapidly changing environments. Proline, an important amino acid, plays an important role in maintaining the metabolism and growth of plants under abiotic stress conditions. Many insights indicate a positive relationship between proline accumulation and tolerance of plants to various abiotic stresses. Because of its metal chelator properties, it acts as a molecular chaperone, an antioxidative defence molecule that scavenges reactive oxygen species (ROS), as well as having signalling behaviour to activate specific gene functions that are crucial for plant recovery from stresses. It also acts as an osmoprotectant, a potential source to acquire nitrogen as well as carbon, and plays a significant role in the flowering and development of plants. Overproduction of proline in plant cells contributes to maintaining cellular homeostasis, water uptake, osmotic adjustment and redox balance to restore the cell structures and mitigate oxidative damage. Many reports reveal that transgenic plants, particularly those overexpressing genes tailored for proline accumulation, exhibit better adaptation to abiotic stresses. Therefore, this review aims to provide a comprehensive update on proline biosynthesis and accumulation in plants and its putative regulatory roles in mediating plant defence against abiotic stresses. Additionally, the current and future directions in research concerning manipulation of proline to induce gene functions that appear promising in genetics and genomics approaches to improve plant adaptive responses under changing climate conditions are also highlighted.

Proline, a multifaceted signalling molecule in plant responses to abiotic stress: understanding the physiological mechanisms

Glyoxalases are known to play a very important role in abiotic stress tolerance. This two-step pathway detoxifies ubiquitously present cytotoxic metabolite methylglyoxal, which otherwise increases to lethal concentrations under various stress conditions. Methylglyoxal initiates stress-induced signaling cascade via reactive oxygen species, resulting in the modifications of proteins involved in various signal transduction pathways, that eventually culminates in cell death or growth arrest. The associated mechanism of tolerance conferred by over-expression of methylglyoxal-detoxifying glyoxalase pathway mainly involves lowering of methylglyoxal levels, thereby reducing subsequently induced cellular toxicity. Apart from abiotic stresses, expression of glyoxalases is affected by a wide variety of other stimuli such as biotic, chemical and hormonal treatments. Additionally, alterations in cellular milieu during plant growth and development also affect expression of glyoxalases. The multiple stress-inducible nat...

Glyoxalase and methylglyoxal as biomarkers for plant stress tolerance.

https://krishi.icar.gov.in/jspui/bitstream/123456789/63703/1/j.biotechadv.2009.04.001.pdf

Genetic and molecular basis of fragrance in rice.

2-Acetyl-1-pyrroline (2-AP) was identified as the major flavor compound in aromatic rice varieties Tainung 71 and 72. In order to understand the mechanism of 2-AP biosynthesis in aromatic rice, we studied the formation of putative precursors, Δ1-pyrroline-5-carboxylic acid and methylglyoxal. The endogenous Δ1-pyrroline-5-carboxylic acid contents of Tainung 71 and 72 calli reached 191 to 276%, compared to nonaromatic rice Tainung 67. In addition, calli of Tainung 71 and 72 contained 1.30- and 1.36-fold, respectively, higher methylglyoxal levels than that of Tainung 67. Specific enzyme activities of Δ1-pyrroline-5-carboxylic acid-synthetic enzyme including Δ1-pyrolline-5-carboxylic acid synthetase (P5CS) and ornithine aminotransferase (OAT) increased significantly in aromatic rice varieties. The expression levels of P5CS1 and P5CS2 genes were found to be significantly higher in aromatic rice than nonaromatic rice. Results of a tracer experiment with 15N-labeled glutamic acid revealed that the nitrogen atom ...

Biosynthetic Mechanism of 2-Acetyl-1-pyrroline and Its Relationship with Δ1-Pyrroline-5-carboxylic Acid and Methylglyoxal in Aromatic Rice (Oryza sativa L.) Callus

Hui-Su Chuang

Papers

Biosynthetic Mechanism of 2-Acetyl-1-pyrroline and Its Relationship with Δ1-Pyrroline-5-carboxylic Acid and Methylglyoxal in Aromatic Rice (Oryza sativa L.) Callus