Mandayam Parthasarathy, Ph.D. ’66, whose research shifted fundamental understanding of internal plant structures, died Aug. 7 in Ithaca. A professor emeritus of plant biology, Parthasarathy was 91.

“He was gentle and friendly, easy to get along with, but he was also rigorous,” said Robert Turgeon, professor in the School of Integrative Plant Science Plant Biology Section in the College of Agriculture and Life Sciences. “He demanded good work from his students, but he was not caustic. He wanted the work done just so, and the people who worked with him learned that and became good scientists as a result.”

Parthasarathy’s expertise was in electron microscopy, a highly specialized field through which he was able to reveal fundamental insights about the internal structure of plant cells and communication between cells.

Early in his career, Parthasarathy discovered how phloem cells function in plants. The phloem transports sugars, which are created by photosynthesis, through the rest of the plant via tubelike cells separated by end-wall “sieve plates” that look and function like a kitchen sieve. Previous scientists believed the holes in these plates were blocked and debated alternate theories about how plants might transport sugars, said Peter Davies, professor emeritus of plant biology and a long-time colleague of Parthasarathy’s.

Parthasarathy discovered that the plates only appeared blocked because of the way scientists were preparing and studying plant specimens. With the careful preparation of living plant tissue and an electron microscope, Parthasarathy discovered that they were, in fact, open.

“What Partha showed quite nicely is that the blocked plates were an artifact of the way the tissue was prepared, because you’re cutting a tissue and then studying it. But that’s not how things are, alive in nature,” Davies said. “It totally changed the way we understood and taught about sugar transport in plants.”

Parthasarathy also revealed basic insights into the cytoskeleton – the internal structure of plant cells – and the plasmodesmata, which link cells and are important for intercellular communication, including movement of viruses, bacteria and genetic code, said Turgeon, who collaborated with Parthasarathy on some of that research.

“That was very influential work. The structure they came up with was, and still is, the fundamental structure that you see in textbooks today,” Turgeon said. “The plasmodesmata work is significant for a wide variety of fields. Developmental signals go through the plasmodesmata, as well as proteins and nucleic acids. Viruses and bacteria also have to get through the plasmodesmata. His impact stretches across many fields.”

Parthasarathy was also a helpful and willing collaborator, who partnered with colleagues across the university to use the electron microscope, which he maintained for decades.

“Electron microscopy is a very specific and devoted field that requires a lot of training and, I think, a particular kind of person – someone patient and artistic,” Turgeon said. “Partha was excellent at that kind of work.”

“Partha was a delightful colleague and an absolute gentleman,” Davies said. “He was appointed chair of the department as an associate professor, which was unusual, and he had to deal with quite a few difficult situations. He handled them gracefully, was pleasant to everyone and his actions as chair were appreciated by everybody.”

Parthasarathy was born June 18, 1932, in Chennai, India. He earned a bachelor’s degree from Presidency College in Kolkata and a master’s from the University of Pune before completing his Ph.D. at Cornell. Immediately after his graduation in 1966, he joined the Cornell faculty and remained with the university until his retirement in 2005.

Parthasarathy is survived by two daughters, Janaki ’05, MPA ‘09, and Valli ’94.

Krisy Gashler is a writer for the College of Agriculture and Life Sciences.