Crops aimed at feeding an exponentially growing population are often exposed to a variety of harsh environmental factors. Although plants have evolved ways of adjusting their metabolism and some have also been engineered to tolerate stressful environments, there is still a shortage of food supply. An alternative approach is to explore the possibility of using rhizosphere microorganisms in the mitigation of abiotic stress and hopefully improve food production. Several studies have shown that rhizobacteria and mycorrhizae organisms can help improve stress tolerance by enhancing plant growth; stimulating the production of phytohormones, siderophores, and solubilizing phosphates; lowering ethylene levels; and upregulating the expression of dehydration response and antioxidant genes. This article shows the secretion of secondary metabolites as an additional mechanism employed by microorganisms against abiotic stress. The understanding of these mechanisms will help improve the efficacy of plant-growth-promoting microorganisms.

The resistance of malaria parasites towards the current antimalarial therapies continues to fuel the search for new antimalarial drugs, preferably from natural sources. This study aimed to investigate the potential of the dichloromethane extract of Acanthospermum australe to inhibit Plasmodium falciparum heat shock protein 70-1 (PfHsp70-1). The plasmodium lactate dehydrogenase (pLDH) assay was used to determine the antiplasmodial activity of the crude extract against the chloroquine-sensitive P. falciparum strain 3D7. The inhibitory effect of the plant extract on the chaperone activity of P. falciparum heat shock protein 70-1 (PfHsp70-1) was determined using the ATPase, thermally induced luciferase and malate dehydrogenase (MDH) assays. The extract showed a significantly high activity against P. falciparum strain 3D7 with an IC₅₀ value of 1.3 µg/mL. A decrease in thermally induced aggregation of MDH and luciferase was observed when each of the proteins was incubated with PfHsp70-1 only. However, an increased protein aggregation was observed when the proteins were incubated with PfHsp70-1 in the presence of the plant extract. The extract also exhibited inhibitory activity on the ATPase activity of PfHsp70-1. The results obtained from this study suggest that A. australe extract contains compounds that could target malaria parasite Hsp70 functions.