Plant senescence and crop productivity: Journal Club with Peter Venn

Peter Venn, a PhD student working with the University of Sheffield’s P3 research centre, introduced the Grantham Scholars to senescence at this week’s Journal Club. This led to an interesting discussion on how it might be used to make crops more productive.

This week’s paper

Plant senescence and crop productivity by P. L. Gregersen, A. Culetic, L. Boschian and K. Krupinska

Peter Venn

In this week’s Journal Club, we gathered in the new Finlay Library at the Department of Animal Plant Sciences to discuss the potential of senescence to enhance crop productivity. Plant senescence is a controlled aging phenomenon where nutrients are recycled from old, unproductive, or stressed parts of plants and reinvested into growth or seed production. Commonly we recognise senescence as leaf yellowing. In many crops delaying leaf senescence increases yield, while in some cases delayed leaf senescence also increases drought tolerance and performance in nutrient-poor soils. However, the benefits of delaying senescence depend on the plant, the environment in which it’s grown, and the crop being produced.

The review on ‘Plant senescence and crop productivity’ provided a broad overview of senescence, from what it is, to what triggers it, to its effects on yield. It gives many examples of the costs and benefits of senescence in crop production. I hoped that the paper would stimulate a discussion on manipulating senescence in crop breeding and its potential for producing higher yielding crops under drought conditions with less fertilizer input. The paper also raised the topics of GM crops and of beneficial genes that are only found in wild crop ancestors, which we discussed at Hannah Sewell’s recent Journal Club.

Delaying senescence extends the period of time during which seeds are filled with nutrients. This raises a question that relates to James Thackery’s project on seed size – could seeds continue to get bigger if senescence is delayed longer? James informed us that seed size is limited by space within the seed pod; seeds start off hollow and then fill, but the pod won’t get bigger.

The idea that increasing senescence (and nutrient recycling from leaves to seeds) during drought would have a negative impact on yield seemed to most of us illogical, because senescence promotes the recycling of nutrients to support seed production. So, we spent some time unpacking what senescence means to the plant, which under drought, only wants to produce viable seed that germinate, and to the farmer, who is most interested in yield value (seed size, number and nutrition).

We came to the conclusion that when a plant is under drought stress, it only invests enough nutrition into its seeds so that they can later germinate. This means that the seeds aren’t necessarily as big or as nutritious, and therefore valuable, as they could be under non-drought environments. Delaying senescence, on the other hand, produces a higher yielding crop, as the stage where the seed is filled with nutrients is also prolonged.

We wondered, however, what effect delaying senescence has on the fitness of a plant and its seed. Whilst none of us had an answer, we decided that this isn’t necessarily relevant to the farmer, if the crop could be harvested before senescence eventually occurs. An example was given in the paper of tobacco with delayed senescence which had more green leaves at harvest than conventional tobacco. From an agronomic point of view, this meant that there was a greater yield of tobacco leaves, whilst the fitness of the plant wasn’t considered important.

This topic relates to others’ research projects: Emanga, for example, was interested in senescence from the perspective of her pea plants whose lower leaves are senescing. The paper and discussion were also useful to James Thackery, who hadn’t made the connection between senescence and seed yield before. I too hadn’t appreciated the strong connection between the timing of senescence and duration of the seed filling period. I also found it helpful to discuss the potential impacts of my research on controlling senescence at an agronomic scale.