Integrative physiological and transcriptomic analyses reveal divergent chilling tolerance mechanisms in contrasting zoysiagrass cultivars and protective effects of exogenous chitosan
This study elucidates the divergent physiological and transcriptomic mechanisms underlying chilling tolerance in contrasting zoysiagrass cultivars and demonstrates that exogenous chitosan application effectively mitigates chilling injury in sensitive cultivars by enhancing antioxidant capacity and modulating key stress-responsive gene expression.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Lawns that stay green through autumn and into early winter are a rare luxury in many parts of the world. For warm-season grasses, which thrive in heat but struggle when the air turns crisp, the arrival of cold weather is a biological crisis. When temperatures drop to a range that is cold but not freezing, these plants face a silent threat: their cells begin to leak, their internal chemistry gets disrupted, and their ability to make food from sunlight falters. This state, known as chilling stress, forces the grass into a premature dormancy, turning vibrant green turf into brown, lifeless patches. While some varieties of grass have evolved to handle this cold better than others, scientists have long struggled to understand exactly how they do it, or how to help the weaker varieties survive.
In a recent study, researchers at Nanjing Agricultural University in China set out to solve this puzzle by comparing two distinct types of zoysiagrass, a popular turfgrass used on golf courses and sports fields. They pitted a tough, cold-tolerant variety called 'Nannong NT1' against a sensitive variety called 'Nannong LG'. The goal was not just to see which one survived, but to look inside the plants to understand the different strategies they use when the temperature drops. The team also tested a simple, natural substance called chitosan, which is derived from the shells of crabs and shrimp, to see if it could act as a shield for the sensitive grass, helping it withstand the cold that usually kills it.
The experiment began with both grass varieties growing in a controlled environment. The researchers subjected them to a chilling stress of 4 degrees Celsius during the day and 2 degrees Celsius at night, a temperature that is uncomfortable for these warm-season plants but not yet freezing. After six weeks, the difference between the two was stark. The sensitive 'Nannong LG' suffered severe damage, with its leaves turning brown and dying off, while the tough 'Nannong NT1' remained largely green and healthy. When the plants were moved back to warm conditions to see if they could recover, the sensitive variety had a very low survival rate, whereas the tough variety bounced back with ease.
Digging deeper, the researchers measured the internal health of the plants. They found that the sensitive grass was leaking vital fluids from its cells, a sign that its cell walls had been damaged by the cold. It also accumulated high levels of harmful molecules called reactive oxygen species, which are like rust that forms inside the plant when it is stressed. In contrast, the tough grass kept its cell walls intact and managed to keep these harmful molecules under control. Interestingly, the sensitive grass tried to fight back by producing large amounts of protective sugars and amino acids, but this effort was not enough to save it. The tough grass, however, seemed to have a different strategy: it quietly adjusted its internal metabolism to prepare for the cold without panicking.
To understand the "why" behind these physical differences, the scientists looked at the genetic activity of the plants. They read the instructions inside the cells to see which genes were turned on or off. They discovered that the two grasses were using completely different playbooks. The tough grass activated genes related to processing fats and sugars, which likely helped strengthen its cell membranes and maintain stability. At the same time, it slowed down its photosynthesis, the process of making food from sunlight, to avoid damaging itself in the cold. The sensitive grass, on the other hand, tried to boost its production of colorful pigments and antioxidants, but it failed to regulate its basic metabolic processes, leading to a breakdown in its ability to function.
The study then turned to a potential solution for the sensitive grass. The researchers applied a spray of chitosan to the 'Nannong LG' plants before exposing them to the cold. This simple treatment made a dramatic difference. The sprayed plants retained much more water, kept their green color, and suffered far less damage to their cells than the unsprayed plants. After the cold period, the chitosan-treated plants had a survival rate nearly fifty percent higher than the untreated ones. The substance seemed to act as a stabilizer, helping the plants maintain their structure and reducing the buildup of harmful molecules.
When the scientists looked at the genes of the chitosan-treated plants, they found that the spray did not completely change the plant's genetic code, but it did fine-tune a few critical switches. It softened the stress response in the plant, preventing it from overreacting to the cold. Specifically, it adjusted the activity of genes that control how the plant senses stress and how it breaks down stored energy. This suggests that chitosan works by giving the plant a gentle nudge to stay balanced, rather than forcing it to undergo a massive genetic overhaul.
The findings offer a clear picture of how different grasses handle the cold. The tough variety survives by proactively adjusting its internal chemistry and protecting its cell walls, while the sensitive variety struggles to find the right balance and ends up damaged. The study also shows that exogenous chitosan can be a powerful tool for gardeners and turf managers. By applying this natural substance, it is possible to significantly boost the cold tolerance of grass varieties that would otherwise die, extending the green season and protecting lawns in cooler climates. The research highlights that while some plants are naturally built for the cold, science can provide a way to help the rest of them survive.
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