Paradoxical effects of nanomaterials on plants: Phytohormonal perspective exposes hidden risks amidst potential benefits.

The rapid growth of nanotechnology has led to the production of a significant amount of engineered nanomaterials (NMs), raising concerns about their impact on various domains. This study investigates the negative interactions between NMs and phytohormones in plants, revealing the changes in signaling crosstalk, integrated responses and ecological repercussions caused by NM pollution. Phytohormones, which include auxins, cytokinins, gibberellins, abscisic acid, ethylene, jasmonic acid, salicylic acid and brassinosteroids are essential for plant growth, development, and stress responses. This review examines the intricate relationships between NMs and phytohormones, highlighting disruptions in signaling crosstalk, integrated responses, and ecological consequences in plants due to NM pollution. Various studies demonstrate that exposure to NMs can lead to alterations in gene expression, enzyme functions, and ultimately affect plant growth and stress tolerance. Exposure to NMs has the capacity to affect plant phytohormone reactions by changing their levels, biosynthesis, and signaling mechanisms, indicating a complex interrelation between NMs and phytohormone pathways. The complexity of the relationships between NMs and phytohormones necessitates further research, utilizing modern molecular techniques, to unravel the intricate molecular mechanisms and develop strategies to mitigate the ecological consequences of NM pollution. This review provides valuable insights for researchers and environmentalists concerned about the disruptive effects of NMs on regulating phytohormone networks in plants.

Intraspecific variation in sensitivity of high yielding rice varieties towards UV-B radiation.

Effective screening of thirteen commonly cultivated rice (Oryza sativa L.) varieties was carried out to evaluate the varietal-specific differences in morphological, physiological and biochemical responses to various doses of UV-B irradiation (7, 14, 21 and 28 kJ m-2d-1). Determination of UV-B tolerant rice varieties would be helpful in selecting a suitable variety for the areas experiencing higher influx of UV-B radiation. Based on the initial screening of thirteen rice varieties, carried out by analyzing shoot length, fresh weight, photosynthetic pigments and the rate of lipid peroxidation under various doses of UV-B, it was found that Mangalamahsuri, Aathira, Kanchana, Jyothi and Annapoorna were tolerant lines and Neeraja, Swetha, Swarnaprabha and Aiswarya were the sensitive ones. Further screening of these nine varieties was done by analyzing primary metabolites (total protein, soluble sugar and proline content) and non enzymatic antioxidants (ascorbate and glutathione) involved in free radical scavenging mechanism to mitigate the negative effects of UV-B irradiation. Based on the cumulative stress response index (CSRI), the sum of relative individual component responses (total protein, soluble sugar, proline, ascorbate and glutathione content) at each UV-B treatment and total stress response index (TSRI), the sum of CSRI of all the four UV-B treatments for each variety, nine rice varieties selected after primary screening were classified as tolerant (Mangalamahsuri, Aathira and Kanchana), intermediate (Jyothi, Annapoorna, Neeraja and Swetha) and sensitive (Swarnaprabha and Aiswarya).

The imprints of the high light and UV-B stresses in Oryza sativa L. 'Kanchana' seedlings are differentially modulated.

High light and ultraviolet-B radiation (UV-B) are generally considered to have negative impact on photosynthesis and plant growth. The present study evaluates the tolerance potential of three cultivars of Oryza sativa L. (Kanchana, Mattatriveni and Harsha) seedlings towards high light and UV-B stress on the basis of photosynthetic pigment degradation, chlorophyll a fluorescence parameters and rate of lipid peroxidation, expressed by malondialdehyde content. Surprisingly, it was revealed that Kanchana was the most sensitive cultivar towards high light and at the same time it was the most tolerant cultivar towards UV-B stress. This contrasting feature of Kanchana towards high light and UV-B tolerance was further studied by analyzing photosystem (PS) I and II activity, mitochondrial activity, chlorophyll a fluorescence transient, enzymatic and non-enzymatic antioxidant defense system. Due to the occurrence of more PS I and PSII damages, the inhibition of photochemical efficiency and emission of dissipated energy as heat or fluorescence per PSII reaction center was higher upon high light exposure than UV-B treatments in rice seedlings of Kanchana. The mitochondrial activity was also found to be drastically altered upon high light as compared to UV-B treatments. The UV-B induced accumulation of non-enzymatic antioxidants (proline, total phenolics, sugar and ascorbate) and enzymatic antioxidants (ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase and glutathione reductase) in rice seedlings than those subjected to high light exposure afforded more efficient protection against UV-B radiation in rice seedlings. Our results proved that high tolerance of Kanchana towards UV-B than high light treatments, correlated linearly with the protected photosynthetic and mitochondrial machinery which was provided by upregulation of antioxidants particularly by total phenolics, ascorbate and ascorbate peroxidase in rice seedlings. Data presented in this study conclusively proved that rice cultivar Kanchana respond to different environmental signals independently and tolerance mechanisms to individual stress factors was also varied.