With the help of light we can improve plant growth

An American study provides new information on how plants detect light and grow. The finding could help make more resilient crops

by Matteo Cavallito

 

Higher yields in fields can be achieved by focusing on a sometimes underestimated factor: light. This was claimed by a team of researchers at the University of Wisconsin-Madison who observed the role of an important photoreceptor in plant stems. This discovery, says the study published in the journal Current Biology, makes it possible to expand knowledge about the mechanisms used by shoots to sense light and direct their growth.

Light influences plant growth

Early stand development, or the way plants sink their roots into the soil, is an important indicator of crop success, a statement from the researchers points out. Understanding how photoreceptors influence this stage of growth is therefore of great interest both to scientists and farmers.

When a plant germinates, the authors continue, its stem elongates to emerge from the soil until photoreceptors detect enough sunlight to produce energy through photosynthesis.

However, unexpected events may occur. Sometimes, in fact, the seedlings emerge from the ground, they may be covered by soil again due to various factors such as wind or the passage of some animal. When exposure to light is lacking, the photosynthesis process cannot continue, thus endangering the survival of the plant. And it is that point that a hitherto unknown actor comes into play: cryptochrome-1 (or cry1), the leadind actor in this story.

A decisive photoreceptor

Analyzing the case of Arabidopsis shoots, a model plant, the researchers found that cry1 not only controls the elongation of the upper part of the stem but also helps the plant return to light. Like another photoreceptor called phototropin 1, cry1 acts as a brake by preventing cells from overextending so they don’t grow uncontrollably. When the plant germinates, in other words, it prevents it from fully elongating, conserving energy and stem length in reserve.

In this way, if the seedling is re-covered, the photoreceptor can stimulate it to elongate further until it emerges from the soil again.

By measuring growth at time intervals of a few minutes using machine learning, the study explains, it was possible to observe the mechanism in detail.

Receptors balance each other

Blue light, that is, the light with greater energy than the others in the visible spectrum, was intercepted by phototropin 1, which “rapidly inhibited expansion” of cells in the hypocotyl, the part of the stem just below the young leaves, in a wide area located about 1 millimeter below the stem tip (at the so-called cotyledonary node). At the same time, the same receptor stimulated the growth of other cells that had not yet elongated, in a narrower area closer to the stem tip.

At the same time, “Nuclear cry1, and not its cytoplasmic pool, counteracted the phot1-initiated expansion of the small cells in this apical region, preventing them from entering the more basal elongation zone.” Cry1, in other words, balanced stem elongation by stopping growth in one specific area and stimulating it in another resulting in a more balanced expansion.

The importance of the discovery

The research thus provides previously unpublished details about the phenomenon. “For the first time, we realized that the effect of these photoreceptors is not everywhere along the stem and that different photoreceptors control different regions of the stem,” explained Edgar Spalding, professor emeritus of botany at the University of Wisconsin-Madison and co-author of the study with researcher Julian Bustamante and data scientist Nathan Miller. The results, the authors conclude, thus open new perspectives on the study of seeds and the role of cry1 in helping the most vulnerable crops achieve adequate stem length while conserving the energy needed to re-emerge should they be covered by soil.