The defensive benefit and flower number cost of selenium accumulation in Brassica juncea

Selenium is an essential element for animal health, but it can be also be toxic in high concentrations. Plants are known to exploit this by storing high levels of selenium in their leaves and effectively poisoning herbivores and pathogens. Yet, there can be costs associated with accumulation of selenium in plant tissues, including oxidative stress and reduced growth rates. Selenium can also replace sulfur in proteins, resulting in protein malformation and impaired protein function. Therefore, it is important that plants strike a balance between the positive and negative impacts of selenium accumulation, optimising the benefits of herbivory protection whilst preventing oxidative damage and growth impairment.

Brassica juncea, the study species, is known to accumulate selenium in its tissues to protect from herbivory. Image: Petr Pakandl / Wikipedia.

In a new study published in AoBP, Steven & Culver investigate this balancing act in detail in brown mustard (Brassica juncea). Specifically, they explored the lower limits at which selenium concentration serves as a defence against herbivory and whether these concentrations showed a cost to plant growth. The authors found that brown mustard plants that absorbed selenium from the soil and accumulated it in their leaves were in fact eaten less by a moth larva (Pieris rapae).  However, at high concentrations of selenium plants also made fewer flowers. In this study, accumulating selenium protects B. juncea plants from herbivores, but it may come at a cost in reproduction. The authors conclude that indeed, a balance between defence and toxicity may favour the maintenance of intermediate levels of selenium concentration in tissues of selenium accumulators such as B. juncea.

Researcher highlight

Janet Steven was raised in West Virginia and graduated from Davidson College with a Bachelor’s of Science in Biology in 1996.  She received a PhD in Botany from the University of Wisconsin-Madison in 2003 and conducted postdoctoral research at Indiana University.  She began her liberal arts teaching career at Sweet Briar College, and is currently an associate professor at Christopher Newport University in Newport News, Virginia.

Janet is a plant evolutionary ecologist with an interest in microevolutionary processes. She is invested in undergraduate research and teaching students to become better scientists. She also serves as director of the Master’s in Environmental Science at Christopher Newport, and values the role of research and scientific rigor in environmental careers.