The anatomy of petal drop in sunflowers

Study finds cell division at abscission zone of short-lived cultivar occurs earlier than in long-lived variety

ITHACA, NY - Despite their consumer popularity as cut flowers, some sunflowers are difficult to market because of their tendency to lose petals soon after their flowers open. This characteristic, "petal drop", which in some varieties can occur within a day of the flowers' opening, ruins the appearance of sunflowers and damages their market value. Sunflower growers interested in finding cultivars that are less prone to this condition have had limited information about petal drop, but a new study in the Journal of the American Society for Horticultural Science contains findings can inform both sunflower breeding programs and consumers' choices.

Joyous Suiyigheh Tata and Hans Christian Wien from the Department of Horticulture at Cornell University studied the abscission zone, a differentiated region where petal drop initiates, at the base of petals of sunflower florets in two different cultivars. "We wanted to determine if differences in the abscission zone among sunflower cultivars were correlated with differences in timing of petal drop," the authors said. Two pollen-free hybrid sunflower cultivars were selected for evaluation: Procut Bicolor, which loses its petals easily, and Procut Yellow Lite, which holds its petals much longer.

For the first experiment, the researchers measured separation force for the two sunflower cultivars using a modified soil cone micropenetrometer, an apparatus that measures separation forces in the opposite direction. "The separation force experiments showed that detachment forces switched from an initial high to low in both cultivars because of the maturation of the separation layer. This maturation occurred earlier in the cultivar that is first to lose its petals (Procut Bicolor)," the authors said. They noted that there were no force readings for the short-lived cultivar on day 9 and day 12 because the flower had already wilted.

"In the second experiment, we studied the changes in the anatomy of the petal-achene juncture of the two cultivars," the scientists explained. Three stages from Procut Bicolor (PBC) and four stages from Procut Yellow Lite (PYL) were studied. These stages represent a time course with physiological relevance; when the flower just opens (anthesis), 8 days (the end of flower life for PBC), and 12 days (the end of flower life for PYL). The study also included analyses of petal anatomy at 4 days after harvest. The "end of flower life" was defined as the time when detachment force equals zero; when simply touching the petals caused them to fall off easily. Results of the analyses showed that cell division at the abscission zone of the short-lived cultivar occurred earlier than in the long-lived cultivar. "These results reveal that there was a difference in timing in the formation and maturation of the separation layer between the two cultivars," the authors said.

Interestingly, analyses showed that the mean "break strength" of cultivars in the yellow group was higher and significantly different from cultivars in the orange and bicolor groups, which were in turn higher than cultivars in the red group. Mean vase life (12 days) of the sunflowers in the yellow group was longer than cultivars in the orange group (10 days), while the vase life of the orange group was longer than cultivars in the bicolor group (9 days). The vase life of the red cultivars was shortest at 8 days. "We found that vase life has a strong relationship with flower color; the darker cultivars in the study had a shorter vase life compared with the lighter cultivars," the scientists remarked.

"The anatomy of petal drop in sunflower is similar to the majority of established descriptions in other species; the process involves the separation of four to five rows of smaller transversely oriented cells that lay horizontally across the diameter at the juncture between the petal and the achene, the separation layer," the authors said. "The concept that the timing of the maturation of the separation layer in the abscission zone helps determine the timing of petal drop is strongly supported by both the physical and anatomical investigations."

The authors concluded that the regression equation and results from the petal detachment force experiments can be used to screen sunflower cultivars in order to determine groupings of short-lived vs. long-lived cultivars. They said that the study contains beneficial information for sunflower breeding programs working to improve the breed's longevity, which can ultimately lead to increased sunflower sales.

Source: ASHS

What it takes to heal a disaster-ravaged forest: Case study in China

Jindong Zhang, a post-doctoral research associate in CSIS, spent several months over a period of four years in Wolong dodging landslides, mudslides and rubble strewn roads to survey forest recovery at a finer scale than can be observed from satellites and getting a better handle on the nuances of tree species, height and soil conditions. The data was then combined with that from satellite imagery.

Recovering from natural disasters usually means rebuilding infrastructure and reassembling human lives. Yet ecologically sensitive areas need to heal, too, and scientists are pioneering new methods to assess nature's recovery and guide human intervention.

The epicenter of China's devastating Wenchuan earthquake in 2008 was in the Wolong Nature Reserve, a globally important valuable biodiversity hotspot and home to the beloved and endangered giant pandas. Not only did the quake devastate villages and roads, but the earth split open and swallowed sections of the forests and bamboo groves that shelter and feed pandas and other endangered wildlife. Persistent landslides and erosion exacerbated the devastation.

Typically such natural damage is assessed with remote sensing, which can be limited in fine details. Scientists at Michigan State University (MSU) and in China embarked on a dangerous boots-on-the-ground effort to understand how well the trees, bamboo and critical ground cover were recovering. Their work, which is relevant to disaster areas worldwide, is reported in this week's Forest Ecology and Management.

"Across the world, people are investing billions of dollars to protect valuable natural areas, as well as making enormous investments in restoring such areas after natural disasters," said Jianguo "Jack" Liu, director of MSU's Center for Systems Integration and Sustainability, and a co-author. "It's important we develop ways to understand the fine points of how well recovery efforts are working, so we can direct resources in the right places effectively."

Jindong Zhang, a post-doctoral research associate in CSIS, spent several months over a period of four years in Wolong dodging landslides, mudslides and rubble strewn roads to survey forest recovery at a finer scale than can be observed from satellites and getting a better handle on the nuances of tree species, height and soil conditions. The data was then combined with that from satellite imagery.
What was found was that much of the natural areas were on the road to recovery, and that China's $17 million effort at replanting native trees and bamboo were helping in areas handicapped by poor soil and growing conditions.

"Our evaluation of the Wolong restoration project will have a guiding role in the restoration scheme areas across the entire area affected by the earthquake, Zhang said. "Our study indicated that forest restoration after natural disasters should not only consider the forest itself, but also take into account the animals inhabiting the ecosystem and human livelihoods."

They also noted that such efforts could benefit from more targeting of areas most favored by pandas. The replanting efforts were done by local residents.

"We witnessed pretty intense periods when it seemed like everyone in the target areas were out planting," said co-author Vanessa Hull, a CSIS doctoral candidate who studies panda habitat in Wolong. "My field assistants also joined in on the village-wide efforts. It was pretty neat to see."
But a potential downside to such efforts was that most of the available labor was near villages, and pandas shy from human contact. That meant that some of the best assisted-forest recovery was in areas not favored by pandas. Hull noted, however, that there could be an upside to that. Healthier forests could mean local residents have less need to venture into more far-flung panda-friendly forests.

"We wanted to know if the benefit of this effort was matching up to the investment -- which was
significant," Hull said. "It's an important question, and the world needs good ways to evaluate it as natural disasters are growing in frequency and intensity."


Source: Michigan State University
Summary: Recovering from natural disasters usually means rebuilding infrastructure and reassembling human lives. Yet ecologically sensitive areas need to heal, too, and scientists are pioneering new methods to assess nature's recovery and guide human intervention. A new study focused on the epicenter of China's devastating Wenchuan earthquake in 2008, a globally important valuable biodiversity hotspot and home to the beloved and endangered giant pandas. Not only did the quake devastate villages and roads, but the earth split open and swallowed sections of the forests and bamboo groves that shelter and feed pandas and other endangered wildlife. The study indicated that forest restoration after natural disasters should not only consider the forest itself, but also take into account the animals inhabiting the ecosystem and human livelihoods.