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Sweet success in Texas.

For Sarah E. Lingle, supervisory plant physiologist at the Subtropical Fruit and Vegetable Research Laboratory at Weslaco, Texas, the data was unexpected. But she didn't doubt its accuracy. Instead, she would have to revise her hypothesis - almost reverse it, as a matter of fact.

Lingle's research was aimed at finding the key biochemical steps in the ripening of sugarcane and the genetic mechanisms behind them. Such information could facilitate the selection or development of sugarcane varieties with higher concentrations of sucrose. Her hypothesis concerned the role of an enzyme called sucrose synthase in the ripening process.

Studies by other scientists suggested that the sucrose synthase enzyme - which appeared to break sucrose down so that it could be metabolized by the plant-was more active in immature, rapidly growing sugarcane stems. Such tissue exhibited higher sucrose synthase activity, according to the studies, and was therefore better able to import sugar from the leaves.

If so, Lingle reasoned, the enzyme's activity should decrease when the tissue was no longer growing and was ripening instead. More sugar would then accumulate in the mature, ripening stem since it wasn't needed elsewhere.

But that was not the case. Nor was the premise correct.

"We found that ripening was associated with an increase only in the percentage of stem sugar that was sucrose," says Lingle, "not an increase in the sugar itself."

According, to Lingle, sucrose synthase activity turned out to be highest in mature stem tissue, not the immature, growing tissue as previously thought. Evidently, ripening in sugarcane was not caused by unmetabolized sugar going to mature stems for storage.

"Our data suggest that ripening in sugarcane is caused by something else that happens to the sugar when it reaches a particular tissue," she says. "It may be related to changes in sucrose synthase activity, but we're not sure. That's one of the things we'll be looking at next."

A significant portion of the data used by Lingle was gathered by Ruben Salinas, Jr., a recent high school graduate who worked at the laboratory last summer before beginning his freshman year as a pre-med student at Texas Christian University.

"We were fortunate in having Ruben," says Lingle. "He was a big help to us. He proved to be a quick learner, was analytical, and accuracy was clearly important to him. I like to give people as much responsibility as they are willing and able to handle, and I was quite comfortable leaving certain aspects of the project up to him."

Ruben's responsibilities at the laboratory included chemically extracting enzymes from sugarcane tissue and conducting spectraphotometric analyses of these enzymes as well as ion chromatographic analyses of sugar from the same tissue.

"At first I felt a little overwhelmed by all the instrumentation and the prospects of having to learn how to operate it," he says. "I'd been in chemistry labs in high school, but nothing like this. The first time I was here, I can remember my nervousness on seeing radiation warning signs. I knew that radioactive isotopes were commonly used in scientific research, but I was still relieved when Dr. Lingle assured me that she would be the one handling them."

Ruben Salinas, Jr., is a first generation American, the oldest of four children of Ruben and Olga Salinas who immigrated from Mexico in 1973.

Ruben Sr. worked as a heavy equipment operator on road construction. Olga made ends meet with sewing jobs. Neither of them spoke English when they came to the United States; Spanish is still the language of choice in their home. But both were determined that their children have all the opportunities that citizenship and a good education can offer.

That he did, graduating fifth from the top of a Weslaco High School senior class of 491. He also rose to the rank of battalion commander of the school's Army ROTC and will be receiving an ROTC college scholarship beginning his sophomore year.
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Title Annotation:biochemical aspects of the ripening of sugarcane
Author:Miller, Steve
Publication:Agricultural Research
Date:Apr 1, 1992
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