Effects of long-term successive subculture on phenotype, organogenesis capacity, and genetic stability in pear
This study demonstrates that long-term successive subculture of pear 'Qingzhen D1' induces phenotypic and physiological changes linked to altered hormone levels and a specific non-synonymous mutation in the cytokinin oxidase/dehydrogenase (CKX) gene, while maintaining overall genetic stability and ploidy.
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
Plants are often grown in laboratories not just to study them, but to make more of them. This process, known as tissue culture, allows scientists to take a tiny piece of a plant and grow it into a full, healthy clone. It is a vital tool for farmers and breeders who need to produce thousands of identical trees quickly, especially for crops like pears that do not always grow true to type from seeds. However, keeping these plants alive in a lab requires a routine of moving them to fresh food every few weeks, a step called subculturing. While this keeps the plants growing, there is a lingering concern among scientists: does this endless cycle of moving and feeding change the plants in subtle ways? Over many years, could these repeated steps accidentally alter the plant's appearance, its ability to grow roots, or even its genetic code? Understanding this is crucial because if the plants change too much, the uniformity that makes tissue culture valuable could be lost, potentially affecting the quality of the fruit trees grown in orchards.
A team of researchers at Qingdao Agricultural University set out to investigate exactly how this long-term routine affects pear plants. They focused on a specific type of pear rootstock called 'Qingzhen D1', which is used to control the size of the tree. The scientists compared two groups of these plants: one group that had been in the lab for only three months, representing a fresh start, and another group that had been continuously subcultured for five years. They wanted to see if the five-year-old plants looked different, grew differently, or carried hidden genetic changes compared to their younger counterparts.
The results showed that the long-term plants had indeed changed, but in ways that were surprisingly specific. About one in five of the older plants developed leaves with deep lobes, a shape they did not have when they were new. Under a microscope, the researchers found that these older plants also had significantly more tiny pores on their leaves, called stomata, which are used for breathing. Despite these changes in leaf shape and breathing pores, the overall size of the plants, including their height and stem thickness, remained exactly the same as the younger plants. The internal structure of the leaves and stems also showed no difference, suggesting the changes were focused on the surface features rather than the plant's core architecture.
Perhaps the most striking discovery was how much better the older plants performed at growing. When the scientists tried to multiply the plants by cutting them and putting them in new pots, the five-year-old group produced more than twice as many new shoots as the fresh three-month group. They also rooted much more easily; while only three out of four of the new plants grew roots, every single one of the long-term plants successfully developed a root system. This meant that the plants that had been in the lab the longest were actually more vigorous and easier to propagate than the fresh ones, a finding that challenges the idea that long-term culture always leads to weaker plants.
To understand why these changes happened, the researchers looked inside the plants at their chemical makeup. They found that the long-term plants had higher levels of certain natural growth hormones, specifically those that encourage cell division and shoot growth, while levels of a hormone that helps with root elongation had dropped. This chemical imbalance seemed to drive the changes in leaf shape and the increased ability to multiply. The team then used advanced genetic tools to check if the plants' DNA had been scrambled by the years in the lab. They confirmed that the number of chromosomes remained stable, meaning the plants were not genetically chaotic in a way that would make them sterile or unviable. However, when they sequenced the entire genetic code, they found that small, specific mutations had accumulated over the five years.
Among the thousands of tiny genetic changes found, the researchers identified one specific mutation in a gene responsible for breaking down growth hormones. This gene, which normally acts like a cleanup crew to remove excess hormones, had a small error that made it less efficient. Because this gene was not working at full capacity, the plant kept more of the growth hormone than it should have. The scientists tested this theory by inserting the mutated gene into tobacco leaves and found that it indeed failed to break down the hormone as well as the normal version did. This suggests that the long-term routine of feeding the plants in the lab led to a buildup of hormones, which in turn caused a genetic mutation that made the plants even more sensitive to those hormones, creating a cycle that resulted in the lobed leaves and the super-charged ability to multiply.
The study concludes that while long-term subculturing does introduce genetic changes, the pear plants did not lose their fundamental stability. Instead, they adapted in a way that made them more productive for cloning, even as their leaves changed shape. The research highlights a direct link between the chemical environment of the lab, the genetic mutations that arise from it, and the physical traits of the plant. This knowledge helps scientists understand how to better manage tissue culture, ensuring that the plants they produce remain healthy and true to their intended purpose, even after years of laboratory life.
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