HERBICIDAL EFFECTS OF THE DIPEPTIDE ALANINYL-ALANINE ON PERENNIAL RYEGRASS (LOLIUM-PERENNE L) SEEDLINGS

Corn gluten meal (CGM), a by-product of corn (Zea mays L.) wet-milling , has been shown to be an effective, natural preemergence herbicide an d fertilizer for various plant production systems. Alaninylalanine (Al a-Ala), along with four other dipeptides were isolated from hydrolyzed CGM and identified as being the inhibitory compounds. The herbicidal effects of these natural compounds are seen as growth-regulating root inhibitors that have minimal effect on shoot growth at low concentrati ons. However, little is known about the precise inhibitory action of C GM or Ala-Ala. The objective of this research was to elucidate morphol ogical and anatomical differences in perennial ryegrass (Lolium perenn e L.) seedlings treated with Ala-Ala by means of light and transmissio n electron microscopy, as well as autoradiographic studies using [H-3( +)]-Ala-Ala. Root length was reduced by at least 42% at all treatment concentrations when compared with the control. The treated root tips w ere observed to be devoid of cellular components, specifically discern ible nuclei and mitotic structures, with an overall loss of cytoplasmi c integrity. Treated root tips had cell wall abnormalities, including uneven thickening and breakage, especially in the epidermal and the ad jacent cortical cells. Autoradiographs suggested that, at treatment co ncentrations causing epidermal damage, there was minimal inward moveme nt of the dipeptide. At low treatment concentrations, root tip epiderm al necrosis was not evident, and inward movement of the dipeptide was not impeded. The herbicidal effects of the dipeptide, Ala-Ala, on trea ted perennial ryegrass roots were numerous. Higher concentration level s seemed to cause more of an epidermal necrosis, whereas, lower concen trations produced more subtle effects to the cellular processes.