Abstract
Arabidopsis thaliana L. is a model plant but little information is available about morphological root changes as part of a phytohormonal common response against both biotic and abiotic stressors. For this purpose, two-week-old Arabidopsis seedlings were treated with 10 μM CdSO4 or infected with CMV. After 12 days the entire aerial parts and the root system were analyzed, and the presence of CMV or the accumulation of Cd were detected. Microscopic analysis revealed that both CMV and Cd influenced root morphology by a marked development in the length of root hairs and an intense root branching if compared to controls. Among the three treatments, Cd-treated seedlings showed a shorter root axis length and doubled their lateral root diameter, while the lateral roots of CMV-infected seedlings were the longest. The root growth patterns were accompanied by significant changes in the levels of indole-3-acetic acid, trans-zeatin riboside, dihydrozeatin riboside, as a probable consequence of the regulation of some genes involved in their biosynthesis/degradation. The opposite role on root development played by the phythormones studied is discussed in detail. The results obtained could provide insights into novel strategies for plant defense against pathogens and plant protection against pollutants.
Highlights
Many factors, both biotic and abiotic are causes of plant stress and can decrease plant growth and productivity
Arabidopsis by Reverse Transcription Polymerase Chain Reaction (RT-PCR). 1, no fragment derived from negative control; 2, no fragment derived from shoots of healthy control; 3, no fragment derived from roots of healthy control; 4, DNA fragment of 513 bp derived from shoots of Cucumber mosaic virus (CMV)-Fny infected Arabidopsis seedlings; 5, DNA fragment of 513 bp derived from roots tissues of CMV-Fny infected Arabidopsis seedlings; M, 100 bp DNA Ladder (New England BioLabs Inc., USA); (B) Levels of Cd in shoots and roots of Arabidopsis seedlings treated with 10 μM CdSO4 (Cd)
Cadmium-exposed seedlings efficiently absorbed Cd, that accumulated in roots and was partly transported and stored in shoots, where it was found in lower concentration (57% of the value found in roots) (Figure 1)
Summary
Both biotic (pathogens, insects, nematodes) and abiotic (e.g., wounds, pollutants, thermal, water and nutritional imbalances, environmental contaminants) are causes of plant stress and can decrease plant growth and productivity. As a response to viral infection, plants may compensate with a broad range of cellular processes by up- or down-regulating certain genes, changing the levels of substances implicated in plant defense pathway, increasing the levels of reactive oxygen species (ROS), activating specific transcription factors, defense-regulated genes, heat-shock proteins, and enhancing the transport of macromolecules, enzymes, and phytohormones involved in defence signaling pathways (e.g., salicylic acid, SA; jasmonic acid, JA; ethylene, ET) [1,2,3]. The involvement of auxins (in particular of indole-3-acetic acid—IAA, the most widely auxin in plants) and of cytokinins (CKs) in viral pathogenesis has been poorly studied [4]. The ability of viruses to significantly interfere with endogenous hormone levels is closely related to a range of symptoms caused by an abnormal growth, as stunting, galls, enations, tissue distortions [5]
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