Ethylene is also produced by plants following infection by a pathogenic organism. This
may be responsible for triggering PAL production in bean leaves following infection with
tobacco necrosis virus,1o2 in tobacco infected with tobacco mosaic viruslo or Pseudomonas
solanacearum,lo4 in sweet potato infected with Ceratocystisjmbriata,8 and in soybean infected
with Helminthosporium carbonum.lo5
It can be shown that ethylene formation in rice is inhibited by R light and restored by a
subsequent exposure to FR. lo6 Is it possible that the effectiveness of FR in certain systems,
in stimulating PAL formation is because of the increased production of ethylene under these
conditions ?